Boldly Going: A History of an American Space Station

[e of pi]

Good morning everyone! This year, @TimothyC and I have gotten a very special present for you all for Boxing Day. We hope you'll enjoy it. Thanks go out to both the usual suspects for editing and image assistance: @nixonshead, @Workable Goblin, @Brainbin, @Usili, and a few unusual suspects too. Post will go up every third day, so look for the next one December 29th. Without further ado, let's get started to boldly launch what no one has launched before...

Boldly Going: Part 1

Ever since the end of the Space Shuttle program, Enterprise has frustrated attempts to tally its successes and milestones, testing the definitions and putting an asterisk next to almost every record. First orbiter to fly? Columbia in 1981, unless you count Enterprise. Longest single mission in space? Atlantis with 24 days on orbit in a single mission, unless you count Enterprise. Fewest missions? Discovery, whose career was cut short in tragedy on her 8th flight, unless you count Enterprise. Heaviest payload carried to orbit by the Space Shuttle? Atlantis with the Galileo probe and its Centaur booster tipping the scale at 28,592 kilograms, unless you count Enterprise. Most crew aboard a Shuttle? Challenger, carrying a crew of ten, unless you count Enterprise. Fewest crew aboard a launch? Columbia’s two-man crews during the STS-1 through STS-4 flight test sequence, unless you count Enterprise. First launch of the shuttle-derived heavy lift vehicle? STS-99-C in 1998, unless you count Enterprise. Last Space Shuttle flying? Atlantis, unless of course you count Enterprise. OV-101’s history reflects the results of a successful improvisation that has left a profound mark on the history of human spaceflight. It holds a place in critical chapters not only of the Space Shuttle program’s birth and coming of age, but also in future steps into space beyond low Earth orbit. The orbiter’s legacy as “Space Station Enterprise” is poised to see it as a nexus for Western space programs for years to come, even as the decisions made forty years ago that saw the program’s birth still live on in the station’s unique capabilities and limitations. OV-101’s history, complex and contradictory as it may be, is adroitly summed up in the program support team’s officially unofficial motto, unchanged for more than three decades: "First to Fly, Last to Land."

Space Station Enterprise is often used as an example of the concept of “technical debt,’ where early decisions about a project can set its fate for years to come. Almost every compromise in the station’s design can be traced to its early legacy, but also the powerful ability to retool the station to meet new challenges which were never envisioned when Enterprise rolled out of the VAB for her first--and only--orbital flight. Originally, the station was born of the collapse of Carter-era detente in the early 1980s, as the new Reagan administration began to once again see space as a critical frontier in fighting communism. In addition to the military Strategic Defense Initiative, rumors circulated inside the administration’s highest levels of a large Soviet station planned for the mid-to-late 1980s, fed by Reagan’s Hollywood visions of glory and George Bush’s tight connections to and trust of the intelligence community. As it would emerge, the rumors were conflations of actual plans for the modular but Salyut-derived Mir space station and more speculative concepts plans for utilizing the Energia/Buran Shuttle, confusing the size of the latter with the module count of the former. Thus, for a period in 1981 to 1984, a consensus emerged within American intelligence, military, and civilian spaceflight programs that the Soviets might be planning to reclaim some of the glory they lost by not participating in the moon race by launching a space station many times the size of their existing Salyuts or even the lost American Skylab. Facing the possibility of a Soviet station massing as much as 250 metric tons, Reagan was determined that the United States would not fall behind and ordered NASA to begin studies of any practicable effort to match the achievement before the Free World lost the high ground.

With the Saturn V rocket off the table, the only available American launcher capable of matching the proposed payload was the Space Transportation System itself. Though concepts for large clustered rockets similar to Saturn IB but derived from Titan or Delta tankage were being considered for SDI and other projects, they would not be available in time nor would they be able to launch the payloads required to match the Soviet system. Studies immediately focused on two competing methods for utilizing the basic Space Shuttle stack to launch massive, highly-capable stations with minimal modifications. The first was the “Shuttle-C”: a concept involving either a modified orbiter or a new-build propulsion module and fairing to launch a one-time large payload, multiplying the potential performance of the crewed Shuttles by a factor of two or three. While the custom propulsion module was most capable, it would also require significant development and require many years to achieve readiness. The prospect of cannibalizing an existing orbiter was much faster, and for a space station offered the tantalizing prospect of utilizing the orbiter’s existing pressure hull and systems as a basis for a capable station. If a module derived from the European Spacelab was placed in the launch bay during ascent and a derivation of Marshall Space Flight Center’s proposed 25 kW power module deployed along with it, the orbiter’s systems would offer the combined stack access to basic levels of power, data, computers, life support systems, and serve as a structural backbone for future modular expansion. A single launch could carry a station nearly as capable as the entire Skylab into orbit in a single shot, requiring only the expenditure of one of the nation’s precious few orbiters.

The competing proposal was more ambitious, drawing on Skylab heritage. Every launch of the Space Shuttle, after all, would carry almost all the way to orbit the large insulated external tank. This hardware, which unlike the Shuttle was designed to be expended every flight, would offer a cavernous internal volume if accessed by the large inspection manholes located in the intertank and the aft end of the larger hydrogen tank. Even the forward ogive-shaped LOX tank alone would offer more than three times the volume of Skylab ready for outfitting. If even a single tank could be outfitted successfully, it would form the core of a massive American presence in orbit and a base camp for reusing dozens more tanks, offering the possibility of an explosive growth in low-orbital infrastructure. However, adapting the first tank was the challenge. Marshall’s engineers had faced the task of inflight outfitting of a tank head-on only a few years prior for the Skylab program, and had found it to be anything but trivial--a fact best illustrated by the massive simplification of their station design task when they switched from an orbitally converted “wetlab” to ground-integrated “drylab”. Once Skylab could be outfitted on the ground, the tedious tasks of installing fittings for basic operability could be eliminated, enabling a capable station from the start. Even having a pressurized “work shack” for accessing the tanks would offer something better than nothing. The Shuttle external tank could offer none of this--only a massive potential volume and a promise for many more.

The orbiter-derived station became the leading possibility for achieving Reagan’s bold and perhaps over-ambitious vision for an American space station. Some documentation from early in Space Station Enterprise’s development indicates that the decision to present this option may have been as much expectations management as a real advantage for the orbiter-derived station over the external tank wetlab. It appears some NASA station program leaders in Johnson Space Flight Center hoped that the prospect of tearing one of the nation’s brand new spacecraft to its bones for a single flight would put the White House’s urgency in context and divert Presidential attention to more sustainable station programs focusing on assembling many modules using the Space Shuttle. If discouraging the White House was truly their intent, the gambit failed spectacularly.

Even before the formal reports were presented, the White House had not only already seen draft versions of the plans for the Orbiter-derived station, but had also become aware of the potential of the external tank wetlab via the same informal channels. What the external tank wetlab lacked, after all, was a work shed to start its exploitation, something with the endurance to stay up longer than any single orbiter while crews completed the basic outfitting process. The large cabin and cargo bay volume of the Shuttle Orbiter would provide this in spades. An external tank, retained on orbit and modified for future adaption, would make the perfect addition to the Shuttle-derived station: it would result in a combined recorded payload of some 150,000 kg--more than a Saturn V and nearly twice that of Skylab. It would, in a single launch, dramatically exceed anything the Soviet Union could potentially launch for years to come. It was, of course, understood to be a short-term solution, something to buy time for more capable purpose-built modules launched on Shuttle-C or Barbarian rockets, but it would provide a captivating visual of American superiority in spaceflight in its sheer size even if plans to open up the external tank were never fully executed. In late 1982, NASA was directed to select which orbiter would receive the conversion and begin immediate work on this combined station design. NASA’s plans for a more incremental station would fall by the wayside as the new “STS-Derived Spacelab'' received top priority for their operational budget.

 

[TimothyC]

Boldly Going Part 2

With the concept of an orbiter-derived station with a wet lab External Tank receiving presidential priority, NASA was forced to study the combined concept in more detail to present the idea in the best light for Congressional funding of the new STS-Derived Spacelab. The first task was selecting which orbiter in the fleet would be selected for conversion into the core of the new station. Columbia (OV-102), the only orbiter already flying, was spared the dubious honor. Challenger was already torn apart for conversion from the static test article STA-099 into a flight-worthy orbiter OV-099, but was needed urgently in operation to relieve the burden of test flights on Columbia. Long-lead items for the planned Orbiters Discovery and Atlantis (OV-103 and OV-104) were collected, and could have been used for the conversion, building a revised orbiter from scratch. However, NASA knew that these orbiters would represent the “latest and greatest” in the fleet, incorporating many new systems and revisions to the design. These orbiters were therefore those that NASA most wanted protected from the hungry eyes and cutting saws of the newly formed “STS-Derived Spacelab” task force.That left only the orbiter NASA had already once rejected for flight, the free-flight atmospheric test article OV-101: Enterprise.

The first orbiter to fly had been studied and rejected for conversion to a flightworthy status when the decision was made to prepare Challenger for flight. Though capable enough for atmospheric simulations of glide performance, OV-101 lacked many of the systems necessary for flight: functional propulsion mounting systems, thermal insulation, cabin instrumentation, and life support systems. However, with the exception of the propulsion fittings, these were all systems that the newly developed station would need to supplement or replace, either in whole or in part. Enterprise, Johnson decided, would be the perfect sacrifice on the altar of the President’s new direction for space station development. While OV-099 would make the transition to a member of the regular fleet, Enterprise would throw off the judgement of unfit for flight in a different fashion. In May 1983, shortly after the STS-Derived Spacelab received congressional approval to begin work, ownership of OV-101 was officially transferred from the Space Shuttle program office to the newly-formed Space Station Enterprise Program Office. The first piece of hardware to be acquired for the station, Enterprise was now to be made ready for her maiden voyage to orbit.

However, given how closely the two offices were related, the transfer of the orbiter and some associated personnel was entirely a paperwork matter. At the time the decision was made, the orbiter itself wasn’t even on US soil, as it was abroad being exhibited at the 1983 Paris Airshow. During its exhibition, the space station program was publically announced and the first public diagrams of the planned station were displayed, stressing its utilization of the flexibility of the Shuttle program and its large size. NASA might have been internally uncertain of the program’s wisdom, but it was now committed to executing the president’s vision. Its exhibition complete, Enterprise returned to the United States in late June and was delivered to Palmdale to begin conversion work.

Converting a Space Shuttle into a space station was no walk in the park. NASA broke the tasks down into several major projects, which were spread out initially around the country and eventually around the world. The modifications to the Space Shuttle would be centered in Houston, controlled by Johnson Spaceflight Center and their subcontractor Rockwell. The station’s power systems were to be based on the 25 kW power module which Marshall had studied extensively for Skylab expansions or Shuttle free flights. This expanded 50 kW power module would be connected to the orbiter’s power systems, with batteries to replace the complex and life-limited fuel cells. The use of a modular design with ground-integrated but flight-replaceable connectors could allow for future augmentation or replacement as the station grew. Much of the station’s initial scientific value would come from a habitable module mounted inside the payload bay. This would provide space for crew-tended experiments between flights as well as additional volume for experiments undertaken during Shuttle visits to the station, and a start to permanent lab spaces once the station became permanently crewed. The work package was initially assigned to Johnson, along with the task of mounting the power module to the orbiter for launch and executing its deployment.

For both problems, however, Johnson rapidly found interest from the project’s first international collaborators. The European Space Agency had no desire to be left out of the reaction to the potential future Russian stations, and the modules of their Spacelab system were perfect for filling out Enterprise’s payload bay. They offered to build a new Spacelab habitable lab module, LM3, and a payload bay mounting system which would enable the immediate start to construction of the station’s primary structures using a proven design. Payloads could be carried to and from the station using the existing Spacelab Interface Rack (SIR) drawer design. Thus, experiments aboard the station could be regularly rotated by Shuttle crews, and there would be an easy transition from short-duration trials aboard Shuttle to long-duration stays aboard Space Station Enterprise.

Eagerly accepting the European contributions, Johnson would be left to develop the alterations to OV-101 itself. These included revising the middeck lockers to accommodate a more robust life support system, including revisions to the hygiene station and consumables stores to allow them to be serviced in flight. Enterprise’s OMS pods and RCS thrusters were overhauled to increase service life and enable the tanks to be refueled on orbit by visiting Shuttles. The ship’s primary structure even saw major overhauls, most visibly the removal of the unnecessary wings and tiles, but Johnson also was responsible for the addition of a new pressurized tunnel which punched through the belly of the orbiter’s crew module, then though an angled passage between orbiter and tank to connect the mid-deck to the intertank of the station’s external tank. The magnitude of the task was mocked in an internal Space Station Enterprise Program Office newsletter, showing two engineers leaning over an easel on which a blueprint of a Space Shuttle was labeled like cuts of beef.

Marshall, in addition to responsibility for the station’s power systems, would also find itself responsible for the heir to Skylab’s legacy; the conversion of the massive External Tank to orbit-ready hardware. Here, again, the main problem was broken down into nearly endless smaller problems. The intertank was modified with an inflatable circumferential passage, which would deploy inside the station after ascent but allow easy access to the tank as normal for launch preparations. The passage had to be carefully shaped to fit around the massive thrust beam inside the intertank which carried the load from the two enormous Solid Rocket Boosters. Connections were provided to the intertank end of the connecting passage to the orbiter, as well as to the 36” diameter manhole inspection hatches offering access to the oxygen tank in the nose and the massive hydrogen tank below. Finally, a docking port based on the 1973 Apollo-Soyuz Test Project’s APAS system would be provided on the side of the station’s intertank facing away from the orbiter, where a second orbiter could dock. Though belittled as “the hamster tubes,” the nearly 20 meter long tunnels around the intertank and up into the orbiter’s belly posed a major challenge, as they would have to avoid any damage from the vibration and dynamics of a Space Shuttle launch, then deploy the inflatable intertank tunnels automatically in order for the first Shuttle crew to begin inspecting the station.

To conserve budget and reduce risk, investment in modifying the interior of the two tanks was limited compared to Space Station’s predecessor. Even when conceived as a wetlab, Skylab was envisioned to launch with triangular grid floors and permanently mounted equipment hardpoints inside the tank along with their cryogenic contents. In contrast, Marshall planned to fit Enterprise’s tank with only minimal future hardpoints for potential decks or cable runs attached to the tank’s stringers and anti-slosh baffles. Given that Skylab had found installation of more than basic flooring difficult inside a cryogenic tank, Marshall instead focused their efforts on studying and prototyping systems for mounting to the standard tank fittings, and adding the absolute minimum of additional mounting brackets along the walls. Study of the altered propellant flow and slosh conditions induced by flooring materials was judged to be less valuable than considerations for on-orbit assembly of the electrical runs, air ducts, and other systems which would have to be added to bare floors to form a functioning module.

Also competing for focus was a more critical problem: the challenge of adapting the External Tank’s insulation system to something suitable for long term flight. The spray-on foam insulation (SOFI) applied to the tank was a closed cell foam, meaning each cell of the foam became its own pressure vessel in the vacuum of space. As these popped, they could cause chunks to spall from the insulation unpredictably and fill the station’s orbit with as much as two tons of dangerous foreign object debris. Marshall’s engineers went to work examining alternatives to prevent the station from turning into a time bomb, posing a risk to itself and other objects sharing its orbit. Solutions of flight-releasable coverings, discarded during ascent as with early Centaur stages, were considered, but engineers quickly realized that the foam could serve a valuable role as protection from radiation, micro-meteorites, and orbital debris for the pressure wall of the tanks if retained. Thus, the preferred solutions began to include alternate insulations, modifying the foam structure, improving adhesives holding the foam to the tank wall, and the application of various external sealants.

The division of responsibilities reflected the transition of the STS-Derived Spacelab from a knee-jerk presidential reaction to supposed massive Russian space stations into the reality of a new Space Station Enterprise that would be at least an interim goal for the development of space hardware for the agency. NASA was still not uniformly convinced of the viability or value of the concept compared to more traditional stations, but direction from headquarters and a growing momentum within the portions of Marshall and Johnson Space Flight Centers devoted to the Enterprise Program Office provided enough of a counterbalance to avoid any field center revolts against the concept. However, as work began, NASA was about to begin relearning old lessons from Skylab and the orbital workshop. The concept of a “simple” conversion of hardware in space was rarely as simple in practice as it was in bullet points on a viewgraph slide…

 

[TimothyC]

Boldly Going Part 2 Image Annex

These are some of the historical concepts and designs that we drew from when coming up with this timeline. Much like Shuttle-C, the concept of a station derived from the external tank, the orbiter, or both was entertained to varying degrees and with varying details across a broad span of time. We’ve combined several of them, most notably the 1992-3 Ware & Culbertson STS-Lab concept, in creating the configuration for Space Station Enterprise.






Report on Space Shuttle External Tank Applications by Alex Gimarc



Shuttle Derived Space Station Freedom, Space Industries International, Inc./Rockwell International Space Systems Division, presentation materials, n.d. (July 1991).

For more information, see David Portree’s blog post here





US Patent # 5350138



STS-Lab - A low cost Shuttle-derived space station By Ware & Culbertson

 

[e of pi]

Boldly Going Part 3

The scope of the issues encountered as Marshall and Johnson began to allocate work and dig into the challenges of converting the Shuttle stack into a functional space station could hardly be understated. Even in fall 1983, as the project teams were still forming, many argued that the effort of converting a Shuttle into a station would be better invested in a clean-sheet station more like previous studies of Shuttle-constructed designs. NASA had spent a decade imagining how to assemble a station launched with the Space Shuttle, but the Shuttle-converted station was relatively immature. Questions quickly arose if the Shuttle-derived station was truly faster or more capable than a Shuttle-assembled station, and lingering debates on value for money and available schedule margin would haunt the project over the next several years as costs and scope spiraled and budget requests had to be altered in turn. If fears of Soviet stations had never reached their 1984 peak and the true upper limits of Mir planning had been better realized, it is possible that the Space Station Enterprise program might have been abandoned and alternate projects might have replaced it--whether for better or for worse, depending on the premises of various counterfactuals. However, much as the American Shuttle had been mis-identified as a military bomber by Soviet scientists skeptical that Americans would invest such funds and develop such a rocket based on the shoddy mathematical projections of demand which underlay many early Shuttle studies, leading to Energia and Buran, so too were Americans able to convince themselves that Buran’s existence and rumors of its ability to launch very heavy monoblock payloads on Energia must mean that Mir was, indeed, merely the start, another stepping stone to a massive presence in space. It was as much of a fantasy as the legends of the lost city of Atlantis, but it meant the White House continued to evaluate Space Station Enterprise as a priority through critical years as hardware began to be constructed.

The program wasn’t all hassles, however. For every challenge as daunting as the Orbiter system and structural revisions, there was one which was fairly straightforward. In 1984, while Palmdale and Johnson contemplated the first cuts into OV-101’s structures, the production of a permanently-orbital Spacelab module was already underway in Italy. While Marshall wrestled with hamster tube inflatable intertank corridors and the challenges of foam which was too well sealed and yet too poorly attached for long-term use, other teams were issuing final contracts to begin production of the station’s initial 50 kW Enterprise Power Module (EPM), derived from a 25 kW Power Module originally studied for either a salvaged Skylab station or for Shuttle-Spacelab mission extensions. The summer and fall of 1984 would be remembered as the nadir of the program, as Space Station Enterprise managers dodged questions about its justifications and tradeoffs from Congress and internal dissent from other NASA station planners who had seen their concepts discarded for a makeshift alternative.

However, much like the station they would eventually build, the Space Station Enterprise Program Office was only passing a perigee, not seeing their flight come to an end. There was a launch at the end of the tunnel, more real by the day--and if that pressure was immense on the schedule and budget, it was also the lure which drew teams on to solve the challenges of the project in sequence. One by one, systems and subsystems passed from preliminary design reviews to critical design reviews, then into prototyping and fabrication. Day by day, men and women went to work and metal began to be formed into parts. In Michoud, a new External Tank began fabrication, assigned the unused ET-007 number originally assigned to the cancelled final Standard Weight Tank. This unique one-off modified tank would serve as OV-101’s ride to space, and gained many nicknames as it proceeded in halting fashion through both standard and radically altered manufacturing phases at Michoud, gaining nicknames like “The Heavyweight Tank” and “Moonraker”. Meanwhile, the Palmdale team began the modifications to OV-101’s primary structures. Progress, when it came, was immediately visible. Engineers tore apart OV-101’s aft boat tail to begin the installation of a fully-functional main propulsion system, preparing the propellant lines to feed real RS-25s where the orbiter had only ever carried simulators.

The most notable changes which distinguish Enterprise from her sisters to this day came next: the great wings which marked a Space Shuttle were clipped. As with other systems removed from Enterprise such as landing gear actuators and doors, this process was not as simple as cutting torches and saws, as was sometimes joked earlier in the process. The orbiter’s wings and tail were some of the most critical long lead structures, and the addition of an extra set to the spares stockpile for maintenance of the rest of the fleet was immensely valuable.[1] Many of the systems required for flight which would require conversion, such as radiators, tanks for cryogenic fluids, OMS and RCS, radars, and star trackers had simply never been installed. Another notable system which had gone uninstalled during Enterprise’s first time at Palmdale was the Shuttle’s internal airlock, and unlike other systems none would be installed. Instead, an external airlock derived from the same design would be included aft of the Spacelab module, just forward of the mounts for deploying the power module from the bay. With no requirement to land, the bay could be loaded with a mass distribution incompatible with the center of mass requirements for a landing. These limits applied to every regular orbiter even for payloads to be deployed on orbit, in case an abort brought them back to land. One way or another, such landing concerns didn’t apply to Enterprise. Instead, every open compartment could be loaded as necessary as crews tore open Enterprise down the structural level.

Every kilogram saved in removed tiles and clipped wings (and more besides) came back as the station’s hungry systems swallowed the project’s weight margins at a terrifying rate. Six thousand pounds of landing gear was reborn as the mass margin for the new pressure tunnel linking the intertank to the belly of the orbiter and its ascent fairing. Twenty thousand pounds of tiles melted into an entry on a weight and balance sheet and emerged as the margin for the intertank tunnels themselves. Two thousand pounds of fuel cells and related hydrogen tanks were removed, replaced by the tie-ins for the new solar power system Marshall was building to mount in the bay. Twenty thousand pounds of wing and tail structures and actuators would be reborn as modifications to the systems critical to support the orbiter’s flight in her new home--augmented thruster propellant supplies, systems to ease remote operation of the station between crews, tie ins for the power module to the old fuel cell busses, and the systems to resupply everything possible in flight. All told, more than 20 metric tons of additional payload were added through removal of unnecessary systems. Some had to be unbolted, cut, or otherwise removed, as were Enterprise’s wings and tail. Others, like the tiles of the Shuttle’s thermal protection system, were simply never installed since they had been left off for Enterprise’s glide test career. Much of the weight removed came back as ways to enable long-term operation of a spacecraft originally designed for mere weeks in space. The 45-inch diameter fuel cell hydrogen supply tanks were replaced by new tanks of similar volume to augment the station’s oxygen supplies. A 700-pound system was added to interconnect the forward and aft RCS supplies, including valves for resupply tanks to be coupled in the future. Additional water tanks had to be incorporated in the cabin. By 1985, the design had largely stabilized, and with it the total launch weight at nearly 150,000 kilograms--more than the performance of a Saturn V and almost twice the launch mass of Skylab. Major hardware like OV-101 and ET-007 were already in hand for conversion at their respective subcontractors. New design hardware for the conversion like the modified European Spacelab module, the new airlock, the Power Module, the revised crew cabin systems, and the external tank’s “hamster tubes” were beginning to be built in production forms. The slips in the program’s schedule shrank and the launch date began to stabilize. Against all odds, it looked as though a launch might truly only be two years away…

[1]This was historically done in 1985 when Enterprise was delivered to the Smithsonian. All serviceable flight units were removed, including the landing gear struts (some of the most vital and complex forgings on the orbiters) which were eventually used on OV-105. Enterprise received the engineering units from the LGTA-090 test rig in their place. (Jenkins I-448,9)

 

[e of pi]

The complexity of the changes that would be made to OV-101 Enterprise as she would be converted from shuttle to station are best seen with this collection of images taken of the historic orbiters as they were being built, and under maintenance over their lives. You can see how the primary structure is designed, and how the crew module fits into this as a single unit. How much of this would have to be revealed again in the process of tearing Enterprise apart for conversion is left to the imagination of the readers and the nightmares of the Space Station Enterprise Program Office planners ITTL.















When the crew module is inserted, the station Xo=576 bulkhead of the crew module rests against the Xo=582 ring bulkhead, which is part of the primary structure of the orbiter. There’s a removable hatch in the Xo=576 bulkhead which you’ll notice, which is used to gain access to the internal airlock on those orbiters which had them. It was a tight squeeze, but it allowed installing or removing the bulky airlock. It’s a pretty unique view, and though Enterprise never had an airlock here OTL and thus never had to have it removed ITTL, this hatch is relevant for some modifications to eliminate the need for a “bent” passage to the Spacelab module.






The assembly process and some of the scale of the External Tank can be grasped in some of these images of the assembly process, including some unique shots of the tanks before spray-foam application.

 

[TimothyC]

So, Just to give an additional perspective on what the orbiter would have looked like when it came back from Paris to be taken apart, we have these images that were taken by Dennis R. Jenkins at some point:

 

[TimothyC]

Boldly Going Part 4

The early years of Enterprise’s path to flight proceeded against a backdrop of general success in the Shuttle program. The Spacelab module made its orbital debut in a demo flight in 1983, followed by an operational debut on STS-51-B in 1985. This flight and two more Spacelab missions that same year helped clear the path for the three-segment Spacelab module which would be launched aboard Space Station Enterprise to serve as the station’s initial primary laboratory facilities. However, the nine missions of 1985 were put to shame by the planned schedule for the following year. Shuttle flights might be becoming routine, but they were still news, particularly when it seemed every mission broke new ground. Some flight objectives were less immediately gripping, like the launch of one military and two civilian comsats aboard STS-61-H. However, even such “ordinary” missions achieved some note. Two firsts in international crew were racked up with the flights of payload specialists Pratiwi Sudarmono, whose mission to support the deployment of Palapa B-3 aboard STS-61-H made her the first non-Soviet, non-American woman in space, and Nigel Wood, who achieved the honor of the first British astronaut in space overseeing the deployment of the Skynet 4 military communications satellite [1]. Other firsts were carried out to more immediate public notice. Millions of schoolchildren watched live broadcasts of the launch and mission of Christa McAuliffe, which aired on cable news. The next month, Columbia went to space for a look at Halley’s Comet, another mission whose ease of explanation carried it well into public knowledge. Uncrewed exploration allowed the Space Shuttle to again insert itself into headlines with the rapid-fire launch of two large science missions during the 1986 Jupiter launch window. In a demonstration of the quick-turn capabilities of the crews of Kennedy Space Center, the orbiter Atlantis launched carrying the space probe Galileo aboard STS-61-G on May 23rd, within 24 hours of the landing of Challenger after it in turn had carried the Ulysses probe aboard STS-61-F. It seemed every flight brought leaping advances, not just in the ability of even ordinary civilians and scientists to fly into space, but also in dispatching the next generation of exploratory probes through the Solar System. In this, the Shuttle’s crowning achievement of 1986 was opening eyes to the entire universe with the launch and “first light” of the Hubble Space Telescope on STS-61-J.






While these successes were dramatic, the launch of Hubble and the Shuttle-Centaur missions were emblematic of deeper rooted issues both in the Shuttle program and throughout NASA at large. While the capabilities of the Shuttle-Centaur were critical to the successful execution of the Galileo and Ulysses launches, the Johnson and Glenn teams responsible for Shuttle and Centaur respectively had barely come together to carry the project to the pad in time for the critical Jupiter launch window. The two teams had struggled over technical definitions of Centaur as either a “payload element” or a core element of the Space Transportation System. This subtle distinction affected whether control remained with Glenn and the existing Centaur team who were eager to put their skills to work to support the Jupiter probe missions or to Johnson, who were skeptical about the safety of Glenn’s plans and protective of their control of the Space Shuttle program. The two teams eventually resolved enough differences of opinion to establish a working relationship, but the astronauts aboard the flights using Centaur had half-seriously referred to them as “Death Star” missions [2]. The presence of tons of explosive cryogenic propellants inside the Shuttle’s payload bay had weighed on crewmember’s minds, as had the 106% power demanded from the three SSMEs. Reassurances that the risk of the Centaur tankage was a minimal addition to the thousands of tons of equally explosive propellants in the External Tank, or the tons of both explosive and corrosive toxins in the RCS and OMS pods spread around the vehicle, were not particularly effective.

Hubble, for its part, had run into continual issues during development, leading to its launch slipping four years from 1982. The most serious of these was a major flaw found in its original Perkin-Elmer mirror when cross-tested by Kodak as a sop for the cancellation of Kodak’s backup mirror project in 1981. Kodak had quickly found their instruments indicated a problem with the Perkin-Elmer mirror’s shape. Perkin-Elmer, in answer, blamed Kodak’s test instruments, saying it was in effect a “sore loser” trying to cast doubt on the solution of the contract winner. A minor scandal had erupted with the two companies sniping at each other in technical conferences while NASA worked to determine which set of testing instruments was correct. The result after weeks of frantic work by NASA was Perkin-Elmer’s carefully phrased announcement in late 1981 that they had found and corrected an issue in their mirror testing system, but that the telescope would be ready in spite of this for a 1986 launch--a two year slip from the 1984 date which had been targeted only months before. Kodak’s reaction to the statement that their backup mirror’s development was still to be cancelled to “ensure margin for correction of outstanding problems with the primary mirror” were unprintable. The eventual success of Hubble’s debut saw the beautiful images the new telescope revealed make headlines in popular press even as the astronomical community eagerly devoured its early returns. It was enough to cover many sins by the program on its way to flight in the minds of some at NASA Headquarters and in Congressional offices, but the near-failures along the way (like the debates surrounding the safety on Shuttle-Centaur) still lurked in the concerns of those at NASA’s field centers who had been responsible for working past them day-to-day.

Such growing concerns of small issues being papered over in the name of “go fever” were lurking across all of NASA’s programs, including on Space Station Enterprise preparations, as normalization of deviance raced to new heights. The Shuttle had flown ten times in 1986, and yet there were still milestones to clear. As the year raced towards its conclusion, NASA was still aiming to achieve more than one flight in a month. September would be critical to this goal, as NASA aimed for three launches, a campaign that would use each available Shuttle launch pad once: the full set of LC-39A, LC-39B, and Vandenberg’s SLC-6. The end result would be NASA for the first time having two Shuttles in orbit at once. In early September, Columbia launched a DOD mission from Florida (STS-61-N), the secret payload being the first of the SDS-2 military communications satellites. On September 27, only a few days after Columbia’s landing, Challenger launched on STS-61-I carrying the program’s first Indian satellite, INSAT-2, with a plan to retrieve the Long Duration Exposure Facility orbital laboratory satellite. The trio was completed with Discovery’s STS-62-B launch on Sept 29. For the first time, two orbiters were in space together, as the Shuttle program celebrated the twelfth flight of the year, executed in just nine months. However, the failures of program management and normalization of deviance were about to come home to roost. The challenges of supporting two Shuttles at the same time, launching from two coasts within days of each other, pushed NASA’s flight support teams to their limits. Low-priority reviews were abbreviated given the rapid turnarounds and short durations of the missions and the challenges of more critical support of the crew activities on orbit like the deployment of the Ford-built Indian communications satellite, then the maneuvering of Challenger to rendezvous with and retrieve the LDEF. The five day flight was packed and only on Challenger’s final day in space was review of the Challenger ascent imagery completed.

Only with the final report on the STS-61-I launch issued and reviewed was the flight support team belatedly able to begin the detailed ascent imagery analysis for STS-62-B on October 2nd. With just days to go before the planned completion of Discovery’s classified polar mission, the team at Johnson dug into the second set of data gathered from the Vandenberg recorder systems. These were slightly different from the data sets and camera positions they were used to evaluating from Cape Canaveral. Moreover, Vandenberg’s weather proved as much of an impediment as it had been to tracking uncrewed launches. Fog and clouds had lurked on launch day, and made interpreting imagery of the ascent for any off nominal performance or debris more of a challenge than it might otherwise have been. Two days of frantic labor by an already overworked team ensued, including several engineers working straight through the night. They examined shadows in individual frames and the smallest blips on radar to do the usual evaluation that the Shuttle’s ascent had shed no debris or otherwise had a result which might pose a risk to the orbiter. However, tired eyes and 48-hour days were the final critical normalized deviations which robbed Discovery’s crew of their chance to survive. Lost in the clouds and fighting against time, the Johnson engineers didn’t grasp the true size of a chunk of foam shed from the forward bipod, and could only partially model the risks of ET foam and other debris they could spot in the imagery. Their report was inconclusive, but phrased poorly gave false confidence: “Potential impacts identified in data from launch. Indications are some potential risk, but previous data sets indicate models for foam penetration are conservative.” After discussions, the flight directors took this as a clean bill of health. Discovery made her retro burn on October 4th, headed back to Vandenberg. Nothing could have been further from the truth. In fact, the foam which impacted Discovery was more than 600 times larger than any previously modeled, a factor so far beyond reasonable that any conservatism in the model was moot. During descent, the tiles which had been damaged by the impact failed. Scorching plasma penetrated into the primary structure, and despite the best efforts of the orbiter’s commander at the stick, the results were almost foreordained. NORAD radar, following Discovery’s descent, tracked anomalous returns and loss of signal as the orbiter broke up over British Columbia’s Purcell Wilderness. Neither the orbiter nor any of her crew would survive.

[1] From @nixonshead : “This would probably be a Skynet 4 satellite. IOTL Skynet 4B was the first of the series launched, in 1988, but that was a delay due to the need to switch from shuttle to expendable launchers, so 4A would likely be first ITTL. Probably no-one cares, but my first job out of Uni was on Skynet 5, so I have a soft spot for the series ”

[2] For more on this debate in real history, check out the fantastic book “Taming Liquid Hydrogen,” particularly Chapter 6 ‘Centaur Reborn’ and Chapter 7 ‘Eclipsed by Tragedy’.

[NOTE]: In OTL, one of the two Centaur G' units is on display outside of NASA Glenn in Ohio (The other stage was converted to the Centaur T standard, and used to launch Cassini to Saturn):

 

[e of pi]

Boldly Going Part 5

In the wake of Discovery’s loss, NASA was forced to reckon with how far they had pushed their luck, and how close to the edge they had been pushing their teams. The tragedy had many contributing factors, but at its core was management expecting too much, too quickly, from too few personnel. The insufficient post-launch analysis of the tile damage and last-minute risk profiles were cited as critical failures before the decision on landing the orbiter, and had been present in numerous other missions, including the STS-61-I mission which had overlapped with and delayed analysis from Discovery’ STS-62-B. Examining other normalized risks turned up a long list, from nearly-failing SRB seals on more than a dozen missions to Johnson’s and Glenn’s feuds over whether the Shuttle-Centaur’s vent system was sufficient to reduce risks from the crew to an acceptable level. The use of SSME 106% power for Shuttle-Centaur flights and the near-disaster of Hubble’s main mirror were also cited as evidence that it was not simply orbiter operations and launch which were growing increasingly unconcerned with risks to crew and program success. Astronaut Katherine E. S. Roberts, who had been scrubbed from the STS-62-B mission only a few weeks before launch due to a minor health concern, led the presidential commission overseeing and duplicating NASA’s internal investigations [1]. In the end, both the external and internal review came to the conclusion that many of NASA’s recent achievements like Shuttle’s exceptional flight rate, its launches of heavy interplanetary probes with Shuttle-Centaur, and the Hubble mirror near-disaster had been built on a dangerously shaky foundation.

In the wake of this realization, NASA was forced to re-examine every aspect of the Shuttle Program, turning up and addressing concerns not only with tile damage, but also near-burnthoughs of the SRB joints. This was an issue which Thiokol had been trying unsuccessfully to draw attention to for more than a year, and solutions had already been proposed for advanced solid applications.[2] Shuttle program officers were forced to re-examine realistic safe program maximum flight rate, and the level of staff and number of vehicles required to support that level. The result included identifying missions currently manifested aboard the Space Shuttle which could be flown by other (even expendable) launch systems, including much of the Shuttle’s remaining commercial manifest.In the wake of the Discovery tragedy, some programs would be cut as risks and rewards were reweighed. Shuttle-Centaur flights, for instance, were judged as “nice to have” but not “critical.” With the Jupiter-bound missions launched, the projects which had driven the acceptance of their risks were already in the past and their application to ongoing geostationary launches was less impactful compared to safer solid kick stages. Thus, ongoing acceptance of their risk and that of the main engine performance required for their use wasn’t valuable. Shuttle-Centaur was just one of many capabilities to be cut as NASA worked to establish a new normal for mission and hardware development risks in the wake of the Discovery disaster. However, one major hurdle lurked, not in the Space Shuttle Program Office, but in its close sibling, the Space Station Enterprise Program office. After all, perhaps no program better exemplified the ways in which the Shuttle program and architecture had been pressed to the limits than Space Station Enterprise’s attempt to fit a Skylab-equivalent station into the Space Shuttle’s 29,000 lbs payload capacity.

Space Station Enterprise was poised to either be a massive success, or a massive failure. In a single launch, NASA would be achieving the kind of station that the Space Shuttle program had always been assumed to require and was intended to support, helping to justify the program for years to come and dramatically expanding the capabilities of its human exploration program. However, the sacrifice of an orbiter in the process left it a feat impossible to repeat, and one which would have to be flown with no backup. The risk was high: it could achieve a mission impossible to complete any other way, but it was a single roll of the dice risking much of the coming decade. There was no additional orbiter NASA was willing to sacrifice for a second launch the way they had built Skylab A and B. Worse, by 1985, the Central Intelligence Agency and the Defense Intelligence Agency were beginning to carefully admit, though not publically, that their assessments of Soviet station plans were wrong. The Soviets were definitely planning on building a new modular station, but it would follow on Salyut and TKS heritage, not a new Energia-launched module. Energia itself was assessed as being still several years away from debut, and with it any massive 70-ton space station modules to be serviced by the new Soviet orbiter. However, while the original Soviet planning which had spurred Enterprise’s conversion had proven chimerical, there was little recourse to pivot to alternate station designs. As Space Station Enterprise had dragged on, the program had slowly accumulated importance as other station programs were shut out by the ongoing Presidential priority. Alternate station configuration studies had wound down in 1982 and 1983, and the work on Enterprise hardware was largely hyper-specialized to the orbiter conversion, with few applications to a new-build station. By 1986, Space Station Enterprise had grown from a simple expedient to being planned as the cornerstone of long-duration American spaceflight and the key platform for developing experience in orbital assembly and operations.

Ultimately, three factors separated Space Station Enterprise from the pack and ensured NASA re-committed to completing and launching it despite the risks. First, Presidential support for the program had been strong from the start, as President Reagan had personally tied the administration to the station’s concept. Thus, cancelling it would be embarrassing to the White House and critical Congressional staffers who had advocated for the station--in some cases, over NASA recommendations. Second, the development of improvised solutions for seeing Space Station Enterprise to flight had monopolized much of NASA’s space station planning for the last 4 years, leaving both a large sunk cost and few alternatives for what could replace it in any sort of near-term. A new modular station designed to be assembled over a large number of Space Shuttle launches was possible, but would have limited ability to adapt work already completed for Space Station Enterprise. Thus, any such replacement would be starting nearly from scratch, putting activation of such a station perhaps as much as a decade into the future where Space Station Enterprise, even with modifications requested by the Roberts Report and NASA’s internal troubleshooters, could be ready within a year and a half. This was critical to the deciding factor: having some station on orbit was identified as providing a ”safe harbor” function for any future damaged Shuttles [3]. The station, if equipped to feed certain critical consumables to visiting orbiters for extended durations, could serve as a refuge where a crew could await rescue if their original ride to orbit should prove incapable of bringing them home safely, and offer additional systems for inspecting and verifying an orbiter was safe to fly back to Earth.

Thus, the space station program would move ahead even as NASA worked on the Space Shuttle’s Return to Flight (RTF). Indeed, some of the developments made by the Space Station Enterprise Program Office came to benefit the Space Shuttle Program: the investigations of mechanisms for foam loss on orbit and potential fixes would end up contributing to some of the solutions sought to minimize foam loss on ascent, though the full solution (a multi-layer coating including an inner sealant layer and an outer white layer designed to reduce heat absorbed from insolation and minimize tank scorching on ascent) selected for application to ET-007 would remain a one-off solution. Orbiter Challenger flew the Return to Flight mission, STS-36R [4], in May of 1989. Among other procedural changes, Challenger’s launch debuted a new program to focus processing crews on the mission at hand. This “Manned Spaceflight Awareness” program was developed from previous NASA safety programs, but augmented to focus processing and support crews on the mission at hand. As part of this, the program debuted flags for each orbiter, showing its name and a stylized orbiter against a diagonally-divided blue, white, and red background. Similar flags had existed for previous projects, like Gemini, but Challenger’s RTF flight established new traditions [5]. A flag for the specific orbiter assigned flew anywhere work was done to support the flight, from large flags which followed the orbiter from Orbiter Processing Facility to the VAB and then on to the launch pad to small ones which were flown in Johnson’s mission control rooms or draped on walls in support back rooms around the country. Once launched, the flags remained flying as long as the orbiter was, with the flag in Florida moved to a flagstaff near the Shuttle Landing Facility to await Challenger’s return.



[1] She's name-checked as she's the only crew member Wikipedia lists as being assigned to the crew as of STS-51-L OTL. If she was reassigned ITTL, then it's anyone's guess who was on STS-62-B. Unlike Dawn of the Dragon, where I (@eofpi) (by implication) killed John Young and Charlie Bolden…

[2] The SRB design issue was well known at Thiokol, and a solution was already in the planning pipeline. The Filament Wound Case (FWC) SRBs for Vandenberg launches had an extra bit of metal added to the joints to account for the higher flexibility of the cases relative to the steel of the standard units. This addition ended up improving the pressure checks that were conducted in Utah. The reliability of these joints was so improved, in fact, that early in 1986, even before STS-51-L was launched, NASA had directed that the forgings for the next set of SRB segments retain the metal needed to allow the capture feature to be present in the new sections. Had there not been a failure on STS-51-L, by say launching a day earlier (which is the official change in this timeline), it is likely that the boosters would not have been launched in cold weather prior to the new sections reaching operational status, which would have prevented an SRB-caused Loss of Vehicle Accident. The following image, from Jenkins, shows the capture feature, and the geometries of the various designs. For this timeline, presume that the joint geometry of the SRBs settles on something between the FWC and the Proposed RSRM. but the third O-ring is not added (no need for it with the capture feature).

[3] Historically, this concept would come up post-Columbia with the same terminology.

[4] Historically Shuttle launch numbers and STS numbers diverged following STS-9. This is also where the STS-XY-Z designation series started with X being the Fiscal year of the program, Y being the launch site (1 for KSC, 2 for Vandenberg), and Z being a letter representing the number of the flight programed from that launch site in that particular year. Because of the decoupling of the launches and STS numbers, historically the 25th launch was STS-51-L and also STS-33. Following the return to flight, NASA restarted the STS numbering series at the flight number (with later missions still often flown out of order), and all launches that were programed in as being the 26th through the 33rd launches of the program had ‘R’ for ‘Reflight’ appended to their designation. This was even done for STS-29R, which never had a corresponding STS-29 under the original sequence.

Because the time period and launch cout for which the launch number, STS number, and the Mission number were decoupled was larger (32 months vs OTL’s 24 months, and 25 flights vs OTL’s 15) and here, the ‘Reflight’ missions will run from STS-36R to STS-43R.

[5] On the Shoulders of Titans Ch 15-5

So the Gemini flag and the Gemini pennant that had flown over the Manned Spacecraft Center during each of the missions, beginning with Gemini IV were lowered for the last time.[76] ... [76] "Last Flight for Gemini Flags," MSC Space News Roundup, 9 Dec. 1966.

 

[TimothyC]

Boldly Going Part 6

With Challenger’s safe return to Earth after the successful return to flight, the vehicle and her flag returned to the Orbiter Processing Facility. Already, Atlantis and her flag waited in the VAB, mostly ready for their upcoming mission. Among other post-Discovery program changes was the requirement for a second orbiter to be available for an accelerated launch within the time required if an orbiter was unable to return to the ground. Thus, for the first time since “Skylab Rescue,” an entire orbital contingency mission had been prepared: orbiter Atlantis and the STS-300 “Launch on Need” rescue mission. Challenger’s safe return proved STS-300 unnecessary, and freed the largely-completed STS-300 stack (including Atlantis) for their nominal STS-38R flight - the crew launch to accompany Space Station Enterprise. However, while Atlantis was only a few weeks of normal shifts away from launch readiness on the second Shuttle mission since the disaster, its launch would have to work around the complex interactions as the VAB prepared a total of not one, not two, but three STS stacks.

While final preparations were completed on Atlantis’s STS-38R stack in VAB’s High Bay 1, High Bay 3 saw the assembly of the mission which would serve the STS-300 “Launch on Need” role for Atlantis in turn, with orbiter Columbia mated to a stack. In High Bay 2, however, the Kennedy Space Center staff had been slowly accumulating and preparing the results of the Space Station Enterprise Program Office’s efforts beneath the program’s own Manned Spaceflight Awareness banner. Marking the program’s hybrid nature, Space Station Enterprise had a flag nearly identical to the regular orbiters, but bearing a stylized version of the station’s orbital configuration instead of the orbiter OV-101 alone. The rest of the hardware making up the station’s profile had already arrived. External tank ET-007 had been delivered from Michoud in November of 1988, with the completed installation of the “hamster tubes” and the distinctive gleaming white orbital sealant, bearing the name Space Station Enterprise next to the NASA “worm” logo and an American flag stencilled onto the tank in three-foot-high lettering. Once lifted to mate to the SRBs, ET-007 only waited to be permanently bonded to the rest of the future station. In the Orbiter Processing Facility, the final elements of the assembly known as the “Space Station Enterprise core element” were being integrated even as Challenger led the Space Shuttle fleet back to space. The modified OV-101 Enterprise herself had arrived from Palmdale in April 1988, and had spent the last six months being permanently joined and checked out with the rest of the “core element,” including the Spacelab-derived and ESA-built “Leonardo Laboratory Module” (sometimes abbreviated LLM or “LeoLab”), the station’s airlock, and the Enterprise Power Module (EPM). These would be carefully crammed into the payload bay, stuffing it more densely than would have been possible for a standard orbiter’s capabilities and landing center of mass limits.

Because of the removal of OV-101’s internal airlock module, the forward cargo bay pressure bulkhead could be modified in turn to allow a direct, axial passage to the Spacelab module, unlike the elbows and extensions required for normal Spacelab launches. Thus, Leonardo would be attached directly to the aft bulkhead of the former Shuttle’s crew module, saving meters of valuable space. This enabled an extra “segment” of pressurized module to be inserted compared to the standard single or double-length Spacelab modules. Like with normal Spacelab, the first segment when entering from the forward end was the “core” segment, including equipment for sustaining and operating the lab, such as ECLSS, power, and controls. The first segment’s overhead, the side of the module facing out of the bay, was fitted with a window, used for observations of external experiments. The second segment aft was the “experiment” segment, including several drawers for mounting temporary experiments aboard the station and the overhead circular plug was filled by the experiment airlock, a small airlock intended not for crew but for exposing experimental samples. The new third segment added additional experiment spaces, such as a furnace and freezer, but also additional ECLSS. However, the most critical feature was its overhead plug, which mounted another APAS docking port for future station expansion.

At the aft end of the module, a duplicate of the forward cone transitioned to an airlock derived from the standard Spacelab mission airlock. Its placement at the aft end of the module meant that it could be used without interfering with passage between Leonardo and the former Orbiter’s crew spaces, which would now be used as the station’s habitat and control deck. Aft of that was a Spacelab external pallet containing the mounts for Marshall’s Enterprise Power Module, which would be folded out from the bay in flight to deploy four massive 120-ft long solar arrays providing the hungry station with a planned 50 kW of electrical power. This would feed the batteries buried beneath the cargo bay’s floor to provide 25 kW of average power over each orbit. Every remaining volume in the bay was filled with additional systems, such as OMS refueling arrangements, the forward and aft RCS interconnects, systems for refilling the station’s consumables tanks from inside the pressure volume using supplies sent up on future crew missions, and other systems which had to be painstakingly packed around the permanently-installed Leonardo Laboratory and airlock and the deployment systems for the EPM. Installing and testing these systems in the bay consumed the majority of the time OV-101 spent in the OPF, but while crews worked in the bay, others finished checkout of the orbiter’s own converted cabin. In the cockpit, the bulky flight seats had been removed and additional grab handles were mounted to better use the windows for observing operations in the bay and around the station in years to come. The new enhanced life support systems and the improved galley and hygiene stations on the converted middeck drew their own fawning inspection. Where once the exterior skin of the orbiter had been protected by tiles, now they contained the mounting points for the legion of EVA handholds and tether mounts which astronauts would install around the exterior of the Shuttle to enable easier work outside the station.

More than three years after the launch of the first modules of the Mir station which had helped to fuel the Shuttle-Derived Space Station project’s birth six years prior, the core of Space Station Enterprise was rolled out of the OPF in late May of 1989, joining her two sisters in the VAB for the first and last time. Once lifted and mated to ET-007 and her solid rocket boosters, OV-101 completed the major components of the station. Remaining work for technicians included the installation of the pressurized connecting tunnel between the intertank tunnels and Enterprise’s middeck, final checks of system functions, and the last filling of the station’s consumables. Technicians working to prepare the other orbiters welcomed the Space Station Enterprise preparation teams, if slightly uncertain of what to make of the strangely altered stack. Finally, nearly ten years to the day after Enterprise’s use for fit checks before STS-1, OV-101 once again rolled to a pad at Kennedy Space Center. With the hybrid shuttle-station on pad LC-39B, Atlantis and STS-38R was dutifully preparated on LC-39A, while Columbia’s crew prepared for their own hopefully-unnecessary STS-300 “Launch on Need profile.

On June 28, 1989, Enterprise (bearing the mission number STS-37R) waited on the pad for the second launch since the Space Shuttle’s RTF. Her flag flew on the pad for what was intended to be both the first and last time. If her launch succeeded, controllers would proceed to give their attention to getting Atlantis and her crew off the ground. While Enterprise was capable of opening her cargo bay doors (and thus exposing the station’s primary radiators) automatically, nominal deployment of the Enterprise Power Module would require the supervision of astronauts. In the launch configuration, only a quarter of the full solar array (a segment capable of generating 12 kW) would be capable of deployment. Though the power required to support the station with no crew aboard was reduced by two thirds from the roughly 14 kW needed on a normal Space Shuttle orbiter, the average power of the orbiter’s keep-alive systems and the single initially deployed wing would be roughly equal when averaged over an orbit. An extended duration and any unanticipated underperformance of the solar arrays or excessive power draw from the station’s systems could result in depletion of the batteries. Worse, If the initial wing failed to deploy properly, the station’s batteries (though oversized) would be drained by the station’s avionics and basic systems in just 72 hours. Thus, controllers would have a strict time limit to get Atlantis and the STS-38R crew up to the new station, and the plan was to launch Atlantis the same day if possible. With such constraints coming soon on the heels of the Return to Flight, tensions were high, and the pressure was on: if Atlantis wasn’t ready to fly, Enterprise should not launch.

The design of the station’s orbit was permanently shaped by some of the concerns about getting a crew to the station in the first weeks of operation. Three orbital bands had been considered for station operations. The first was the roughly 28.5 degree orbit which was “natural” out of the Cape, and thus offered the largest payload capability for Shuttles rising to the station in the future. This would allow future missions to such orbits (including Hubble Space Telescope servicing missions) to have the station as a backup in case a mission was unable to land on time. The second option lay around 57 degrees, an inclination which would allow overflight of the vast majority of the Earth’s population, as well as offering limited international operations with the Soviet Union and their stations, typically located around 52 degrees. It would also, potentially, allow for Space Shuttles launching from Vandenberg to reach the station, as 57 degrees was the lowest inclination the polar-focused launch site could offer given restrictions on External Tank and Solid Rocket Booster disposal zones. The third band was a compromise, located at about 39-41 degrees. This band would allow imagery of latitudes as high as 65 degrees, meaning the station would be able to image most of the continental United States (and, in turn, would be visible in the sky from the ground by almost all of the country’s population). However, the orbit offered the chance for launches from Florida to “thread the needle” on a southbound trajectory from Kennedy Space Center, flying along a gap in the Caribbean islands to allow a second launch window per day to the station’s inclination. With short launch windows for each attempt, having a second launch window per day would well more than double the chances for getting an orbiter launched to station, as the time between the two windows could be used for troubleshooting and resolving any minor concerns exposed during the initial window. With the criticality of getting the initial crews to station in the shortest possible time, the 39 degree orbit represented the best balance of payload capability, accessibility, and ground visibility for science, resulting in its selection as the station’s orbit around 1988, one of the major decisions about the station’s future during the post-Discovery stand-down.

Now, the benefits of the 39 degree orbit proved to be critical to satisfying the constraints of the station’s power system design. The first countdown on June 28th was aborted over concerns with memory faults in Atlantis computers, resulting in a two-day stand down while the memory units affected were replaced and tested. July 1st saw concerns with Enterprise herself, given issues with level sensors in ET-007, but the issue was able to be resolved by ground analysis in time for the alternate launch window the same day. With the problems resolved, Space Station Enterprise lifted off on July 1st, 1989--six years after the start of the program, and more than a decade after the orbiter at its heart had made the Shuttle’s first gliding flights. In attendance, among others, was former President Ronald Reagan, whose decision to demand NASA place a large station to work with Shuttle into orbit at the earliest possible moment was now being put to the test. Though the general mood in the press area was electric, the former president seemed beatifically calm as he watched the ascent. The boosters cut loose cleanly, and Enterprise’s computers smoothly throttled up the engines in the Space Shuttle program’s first uncrewed launch. Six minutes later, the three SSMEs cut out. The massive engines and external tank were no longer the launch vehicle, but instead payload and structural mass delivered to orbit for utilization.




Images by @nixonshead (AEB Digtial on Twitter)

Edit note: Original version of this post listed the solar arrays as 240 feet long, it should have been 120 feet.

 

[e of pi]

Boldly Going Part 7

With the successful single launch of OV-101 complete, the flight of Space Station Enterprise seemed to clear years of doubts about the program in a single shot. Cheers erupted in Houston, Florida, and in the homes and offices of hundreds of thousands of people who had worked on the station as the ground controllers verified the station was talking to TDRS, then as that relay carried along confirmation that Enterprise had completed the first OMS burn to stabilize her orbit. Soon, a second signal carried confirmation that the orbiter-turned-station’s computers had activated the payload bay door actuators, and onboard cameras downlinked the welcome image of Enterprise’s doors swinging smoothly open in space for the first time. However, the last event on the launch timeline was the most critical of them all--no one on the ground could relax until the computers completed their first programmed activities and deployed the station’s keep alive solar arrays. Too many still remembered that Skylab’s panels had been the source of its problems, and were bracing themselves for a desperate effort to get off Atlantis’s STS-38R launch if anything failed. As TDRS passed the station from satellite to satellite, the downlink capability occasionally faltered. The moment of solar array deployment found the station passing through a window capable of transmitting only telemetry, which recorded the signals indicating that the two solar array sections facing up and out of the bay should have begun to deploy. The Marshall and Houston teams held their breath in spite of the early indications. Deployment motors being triggered meant little, and nothing was for sure until the panels were seen to be open and providing power.

Finally, the downlink flickered back into high-rate capability, and the video picked back up to capture the station’s panels cleanly extending from the Shuttle’s payload bay. Even knowing that the process of fully deploying the keep alive panels would take another half an hour, Houston’s mission control team erupted into cheers--the most critical aspects of deployment were already behind them. Soon, the panels were extended and locked, and life-giving electrical power was beginning to top off the station’s batteries. Space Station Enterprise had reached orbit successfully and now began her service in space. President George H.W. Bush and Former-President Reagan met with Administrator Richard Truly for photographs and speeches commemorating the success of the program. Former-President Reagan’s speech was particularly memorable, as he marked the Space Station Enterprise program’s success as a “Symbol of American Freedom and Enterprise,” comparing it favorably to the capabilities of the Soviet Mir. President Bush’s remarks were more limited, hailing the success, but his speechwriting team had concentrated their superlatives in space for later that month, when they were preparing to announce a major new initiative in exploration. For the moment, the legacy of Enterprise’s launch was marked more by the former president who had initiated it than by the President who would shape its utilization.



With Enterprise’s solar arrays deployed and all STS-37R ascent activities completed nominally, the need for a rushed launch of Atlantis and STS-38R for a mission to “Save Enterprise” as Pete Conrad had once raced to “Save Skylab” was gone. This came as a relief, as unexpectedly poor weather at the Trans-oceanic Abort Landing (TAL) sites haunted Atlantis during the STS-37R countdown. Several press questions and counterfactual what-ifs have hinged on whether NASA would have risked the launch anyway, given the tiny window during launch where such a transatlantic abort was needed and that Space Station Enterprise’s success might have hung in the balance. Then and now, the official NASA stance was and has remained that the safety lessons of Discovery for risk versus reward were clear. Finally, the weather front passed Spain and Morocco, and the first countdown for STS-38R took place on the morning of July 9th. For less complex missions, NASA had cut backup crew assignments prior to the Discovery disaster. Only mission-specific personnel like Payload Specialists were assigned specific backups. Others roles like mission specialists and pilots were assumed to be able to be pulled at need from the general astronaut pool for any specific mission. However, the Space Station Enterprise activation and checkout mission had enough mission-specific complexities driving increased training requirements for the crew that NASA had scheduled full prime and backup crews even before Discovery’s loss.

When first planned in 1986, John Young had assigned himself as commander of the outfitting crew, continuing his record of seeing off the first mission of each new type of module launched aboard Shuttle, including the original STS-1 flight, the STS-9 mission which debuted Spacelab, and the deployment of the Hubble Space Telescope aboard STS-61-J. However, his outspoken critique of NASA management in the wake of the Discovery disaster lead to Young’s promotion out of the astronaut office, effectively removing him from day-to-day management and more relevantly cutting him from the active flight list. He had already personally recruited Joe Engle as the backup commander, and intervened to persuade Engle (who had been considering retiring from spaceflight after the disaster) to instead make one final flight as prime commander for the mission which would commission Space Station Enterprise. Engle’s record was long: three suborbital X-15 flights over 50 miles, a near-miss with lunar missions aboard Apollo 17 which saw him bumped for geologist Harrison Schmitt, and two previous Space Shuttle commands. Moreover, Engle had even flown Enterprise herself in the approach and landing tests of 1977. With the two-year flight stand-down and shifting assignments following the planned Return to Flight, Engle would have his pick of the astronaut corps for the prime crew for the Space Station Enterprise activation mission.

As a result, the rest of the Atlantis flight crew was similarly experienced, including several who had flown multiple Shuttle missions. Experience with the Spacelab module was also sought, given its contributions to the Leonardo Laboratory Module. Pilot Steven Nagel was on his third spaceflight, having previously flown with Spacelab aboard STS-61-A in 1985. On his first spaceflight, he had also had experience with the Robotic Manipulator System (Canadarm) as a mission specialist aboard STS-51-G. On that flight, he had helped use the arm to deploy and then retrieve the Spartan 1 free-flying astronomy satellite. The senior astronaut in the crew by time in space, however, was the prime crew Mission Specialist 1, Owen Garriott. Garriott’s time in the astronaut corps dated back to Apollo, and his experience with Skylab had led to him being appointed as an astronaut liaison to the Space Station Enterprise Program office, providing recommendations for designing the station’s interior for long-duration space operations and consulting on what could be expected for astronauts outfitting a space station while in orbit on missions measuring not days or weeks, but months. There was no one on the flight list more experienced with Enterprise’s new incarnation, and Garriott had been a natural for Young to recruit for the prime crew in 1986. Garriott had eagerly leapt at the chance to implement the results of his hard work by flying to his second space station and adding more days to his existing record: 59 days from his time on Skylab and 10 days from his flight aboard STS-9 with the Spacelab debut. After Discovery, Garriott had (like Engle) been considering retirement, but John Young’s offer to keep him on the Enterprise deployment prime crew had been irresistible for a man who had thoroughly enjoyed his time aboard Skylab more than a decade before. Garriott delayed his retirement by two years to see the mission completed.

Two more veteran Mission Specialists joined the final STS-38R prime crew. The first was Mission Specialist 2 Norman Thagard, who had already flown on three Shuttle missions. This record, accumulating seventeen days in space, included a Spacelab flight, the Galileo deployment mission STS-61-G, and the complex RMS operations of STS-7. As a licensed physician, Thagard would also provide on-orbit monitoring of the crew’s health during one of the longest and most intense Shuttle flights since the program’s start. Mission Specialist 3 on the STS-38R prime crew ended up being Kathryn Sullivan, who had flown EVA during the Hubble deployment on STS-61-J. While Young had slotted her into the prime crew without certainty of her being able to take on the complexity of the Enterprise deployment flight less than a year after the Hubble launch, she was readily available with the additional two-year stand-down. Sullivan had spent the time reviewing EVA procedures for the deployment of Enterprise cargo bay systems and the confirmation of passivating and sealing the massive oxygen and hydrogen tanks of ET-007 both with Garriott and with the last American on STS-38R. This was Mission Specialist 4, rookie Pierre Thuot, who would complete the Extra-Vehicular and Intra-Vehicular Activity specialist team. The final crew member would be the first international visitor to Space Station Enterprise, Ulf Merbold of Germany representing the European Space Agency as a Payload Specialist, drawing on his previous flight with Spacelab. It was a mark of the critical nature of the program that all but one of the crew had previously flown to space, and Engle had trained his crew rigorously for their purpose.

All told, Atlantis carried up seven crew members on her STS-38R mission. The planned mission duration would be 11 days, one of the longest Shuttle missions to date. In the future, Atlantis would be able to draw on Space Station Enterprise to stretch her orbital endurance, using a new system which would allow Atlantis to draw power from the station. In time, all of the remaining orbiters would receive the modification, but Atlantis’ construction after the program’s approval meant she included the capability from the day of her rollout at Palmdale. The capability would not be used on this flight, at least not as originally intended. Still, the fifth mission for the youngest orbiter in the fleet was in many ways what she in particular and her kind in general had been built for: working with a space station for the servicing and deployment of complex payloads in space.

Engle and the rest of the STS-38R crew made rendezvous with Enterprise in the station’s 39-degree, 350 km orbit on July 11, 1989. They had spent their first full day in orbit, Flight Day One, chasing down the station from their lower elliptical parking orbit. The results greeted them on Flight Day Two, July 11th as they approached their target. It was, in one sense, the first arrival of Shuttle at a space station--one of three the Space Shuttle would visit during its history. In another, it was the first rendezvous of two orbiters in space, and the first docking of the Space Shuttle to anything at all. In Atlantis’s cockpit, what it looked like was a tremendous challenge for the flight crew. The enormous white external tank was starkly visible, and the crew called “tally ho” on the station from kilometers out. The station’s bulk grew slowly. With the distance disguised by the clarity of vacuum, Enterprise and the external tank hung in space like a model, looking at first glance no larger than the small satellites Shuttles had deployed and retrieved in the past. It was only in the final minutes, as the distance melted away, that the true scale of the station became clear.



Artwork by: @nixonshead (AEB Digital on Twitter)

 

[TimothyC]

Boldly Going Part 8



The External Tank’s bulk was a familiar one to any orbiter flight crew, who had all had their encounters with the giant orange monsters in ground training and on the ride up the elevator to the pad just days before. However, to find one here, its white anti-popcorning sealants nearly glowing in the orbital sunlight, was almost unnerving. For the first time, a flight crew made rendezvous with something larger than the Space Shuttle, and their challenge was not merely to stash it within the orbiter’s payload bay, but to belly up and dock to it. With Enterprise’s keep alive panels deployed, access to the docking port on the Leonardo Lab Module was blocked, as the port was mainly planned for future expansion. Instead, Engle and Nagel guided Atlantis around the station to the ventral side of the external tank, opposite OV-101. There, a panel replaced in the intertank offered a docking hatch and the access to the inflatable passages located inside the ET’s intertank. Atlantis’s flight crew made the docking look easy, and the orbiter settled into a hard dock. However, before reaching Enterprise’s core modules, the STS-38R crew had to activate, inflate, and verify the so-called “hamster tubes” which Marshall had grafted around the thrust beam inside ET-007’s intertank. The intertank was massive, stretching the full 8.4m diameter of the tank. At the maximum point, the two tank domes allowed nearly the same 8.4m of axial length, but in the middle the two dome ends were separated by bare feet, allowing only enough room for the massive structural beam which carried the thrust from the two Solid Rocket Boosters during Enterprise’s first and only ascent.

Late on Flight Day 2, Owen Garriott opened the hatch between the orbiter and the vestibule, with the station-side hatch still separating him from his second space station. In this awkward liminal space, Garriott and the rest of the flight crew worked to connect the fittings designed to allow Atlantis to inflate and deploy the intertank tubes. The process was the largest flareup of Marshall’s past space station legacy to date. While the Marshall team had expected the first pressure introduced into the intertank passages to easily begin their deployment against the vacuum of space filling the rest of the intertank, the passages did not seem to inflate at first. The crew tried again, but after reaching several psi on the station-side of the hatch, they discontinued attempts for the day to allow ground controllers to work the problem. With Skylab looming large in program leadership minds, the crew resumed the next morning. It was decided that friction between the fabric folds might have exceeded ground expectations, and the crew were directed to simply slowly but steadily supply air into the module. The risk existed that a sudden “snap” to inflation would occur, which could damage the connections between the inflatable tubes and the rigid portions of the station. However, the friction seen as the pressure mounted--literally and metaphorically--reassured controllers that the risk was small. Finally, the tubes began to budge open. After consuming most of Flight Day 3 (putting the mission almost a full day behind schedule), the crew was finally able to open the hatch and gain access to the precious cubic meters of volume they had won in the passages between the tanks. Contrary to the common mental image of inflatable modules as similar to terrestrial bouncy castles, the walls of the module were quite bulky, three redundant bladders, a small MMOD layer in case the rigid outer skin of the intertank structure was holed, and internal insulation and fabric to cushion crew working their way around the circular hallway, a torus roughly two meters in diameter. Netting lined the inner and outer walls, serving both as hand-holds for locomotion and stowage for future gear.

The “hamster tubes” started at the “visitor entrance” to the station and wrapped more than 180 degrees around the intertank to the pressure hull leading to the Core Module Access Passage leading on to Enterprise’s middeck. Two branches broke off as the passage wound under the thrust beam, one each accessing manholes into the LOX and LH2 tanks of ET-007, creating in total roughly 20 cubic meters of pressurized volume at what would, when the tanks were opened, eventually become the core of the station’s traffic patterns. For the moment, these branches were ignored beyond verifying the modified orbitally-accessible manholes remained sealed, as Engle, Garriott, and Nagel worked to make up for lost time. The rigid passage between the intertank and the Enterprise core modules proved much easier to work with. Installed on the ground, clearing through the CMAP was simply a matter of checking and opening two pressure hatches, one on the intertank end and one at the other end recessed into the belly of the former OV-101. After checking air for breathability and watching carefully for any floating particles or debris, the STS-38R crew ended Flight Day 3 by finally gaining access to Enterprise’s mid-deck. The crew celebrated by retrieving a waiting snack of ice cream from the station’s galley freezers before closing the hatches for safety and retiring to Atlantis for a well-earned rest.

On Flight Day 4, the Atlantis crew awoke to the sound of synthesized chimes and the ethereal soprano of Loulie Jean Norman, as a specially-recorded voiceover from William Shatner (never afraid of publicity) offered the crew a benediction for their “ongoing” mission and bid them to go now “where no one had gone before.” (A modification of the script which managed to frustrate many of the same fans the skit was meant to entertain.) Still, taking the words to heart, the crew pressed on into some of the most delicate work of the mission: activating Space Station Enterprise and deploying the rest of its solar power system. When fully active, Enterprise’s base load would rise from the 6 kW sustainable from the keep-alive panels to more than 16 kW (slightly more than Atlantis’s own 14 kW due to the larger volume and modified systems). Once drawn on by the fully active systems, even the station’s nearly fully-charged batteries could sustain it for only a few days. To help bridge the gap, Atlantis’ crew first rigged the connections between Atlantis and Enterprise. With Atlantis’ payload bay carrying no experiments and only a Spacelab module full of cargo for future station crews which the crew had been too busy to begin to transfer, Atlantis could spare a few critical kilowatts to stretch Enterprise’s batteries while the crew went to work to deploy the station’s arrays.

To do so, STS-38R moved their main base of operations from Atlantis to Enterprise for the day, the middeck just different enough in layout to confuse the crew. Larger differences lurked on the cockpit level, which was converted to an “Orbital Operations Center”. The flight chair which Joe Engle had used so long ago was gone, providing more open space on the deck and places to hang checklists and procedure manuals. After getting main power online and getting their first view of the inside of the payload bay since calling tally ho on the station, the STS-38R crew broke up to divide and conquer. While Engle and Merbold went through the process of activating and accessing the Leonardo Laboratory Module, Garriott and Nagel did the same for the station’s robotic manipulator, the CanadArm 2. Unlike the Shuttle version, the station’s arm was capable of detaching from its main base, as it had a grapple fixture at each end which included the ability to draw power from any grapple point which offered it. With this, the arm could be “walked” to multiple locations inside the payload bay and on the structure of the Enterprise Power Module, increasing the reach of the station’s crew. Future plans called for installing bases on the outside of ET-007, allowing the arm to “walk” to within reach of visiting orbiters to hand off future cargo and expansion modules. With Garriott and Sullivan suited and ready for an EVA in case anything went wrong, Nagel and Thuot commanded the Enterprise Power Module to fold up and out of the bay. The hamster tubes appeared to have absorbed any residual “Marshall Luck’ with space hardware, as the primary structural element of the EPM smoothly rotated up and out of the payload bay proper, allowing the “keep-alive” panels to extend over the starboard door sill like an oar. Flight Day 4 was completed by deploying the other solar array wing on the starboard side, adding another critical 12 kW of peak power to the station’s generating capabilities. Even averaged over an orbital night and day, that was enough to reduce the station’s parasitic draw on Atlantis to just 2 kW. Though the STS-38R crew had begun the day almost 24 hours behind schedule, judicious parallel processing by the crew had reduced many of the “catch-up” tasks, as Merbold and the rest of the crew had worked in the LLM even as the operations to extend the solar arrays proceeded only meters behind them in the bay.



Images by @nixonshead (AEB Digtial on Twitter)

 

[e of pi]

Boldly Going Part 9


The crew woke on Flight Day 5 to the Beatles’ 1969 “Here Comes the Sun.” This marked not just the task of finishing the station’s solar array deployment, but a major shift in the mood of the crew and teams on the ground. With Enterprise’s entire starboard solar array wings deployed, the station could be made self-sufficient with no crew aboard. Even if Atlantis finished no further tasks over the remaining five days aboard the station, their major task of securing the station for the future was done. The Beatles’ hopeful melody marked the turning point in the program from securing Enterprise’s deployment to maximizing its success. With the deployment that day of the port solar array wings, Space Station Enterprise had the power to be considered fully operational, and Merbold and Engle continued work to activate the systems in the Enterprise mid-deck, the orbital operations center, the LeoLab, and the airlock. Late in the day, Engle’s crew had caught up to almost every mission milestone. After erasing the 24-hour deficit, the rookies were put to work on “get-ahead” tasks to prepare for Flight Day 6’s main activities: the much-anticipated “Intra-Vehicular Activity” inside ET-007. As the name suggested, this was something which wasn’t quite a spacewalk, but was still quite distinct from operating in a fully pressurized spacecraft. After all, even after days of venting and passivating, ET-007 still contained massive propellant feed and vent lines where ground conditioning systems had fed the tanks full of millions of kilograms of propellants only days prior, then hungry engines had sucked them dry in minutes. All represented potential leak points for the future station. Though there were no immediate plans to make use of the LOX tank’s 560 cubic meters, and even less planning for the massive 1,500 cubic meters of the hydrogen tank, one of STS-38R’s mission goals was to make sure ET-007’s tanks were sealed and pressure-tight, allowing them to be considered fully a part of the station’s volume for future expansion before any errant plans were made.

The crew had spent three days making Space Station Enterprise fit for human occupation, including two spent wrestling with the “hamster tubes” alone. Now, the crew would be confined to Atlantis again while the tubes were used as an impromptu airlock by the two-person team of Garriott and Thuot, with Sullivan suited up in the airlock on Atlantis in case of contingency needs. After checking the hatches to Atlantis and Enterprise proper were closed, the space-suited pair opened the inspection manhole into the LOX tank, their lights catching on the stringers and baffles of the tank. The images captured by each of the pair of the other working backlit against the faintly illuminated tank walls became famous, helping to drive home for those watching on the ground who had not yet grasped the true size of the external tank Enterprise could someday grow into. The pair worked for half an hour around the base of the tank, sealing the main propellant fill/drain line, a job complicated by the baffling designed to prevent sloshing during ascent or geysering during tank fill procedures. Next came another dramatic image, as Garriott (the most experienced of the pair in both EVA and the unusual situation of operating in vacuum in microgravity inside a large but constrained environment) leaped to the top of the tank trailing a tether. There, he jammed a sealant plug into the nose LOX vent where the “beanie cap” had made its usual pre-launch contact to capture boiling LOX and the smaller port where oxygen recirculated from the SSMEs provided tank pressurization. The sealant plugs formed a secondary backup against the valve actuators to ensure the valves would never pass crew breathing atmosphere the way they had once passed gaseous oxygen.

Completing their IVA into the LOX tank, Garriott and Thuot closed and sealed it, then repeated the performance inside the even-larger hydrogen tank, plugging the hydrogen vent valve and pressurization line near the top of the tank, then both made the leap more than 25 meters (nearly twelve stories) to the bottom of the tank to work on plugging the main fill/drain lines. After more than 6 hours of IVA time for the day, Garriott and Thuot finished their work in the hydrogen tank and closed it out as they had the oxygen tank before it. Their work was tested by bleeding a small amount of air into each tank after the intertank was repressurized, to be monitored over coming days and weeks. Still, the final results wouldn’t come until increases in the station’s onboard consumables could allow more precious breathing gasses to be wasted pressurizing unused volume. Nearly eight hundred kilograms (800 kg) of air would be required to fully fill the LOX tank, with just over two thousand kilograms (2,000 kg) required for the hydrogen tank. Even sparing 280 kg to reach 10% final pressure was enabled only by the consumables brought by Atlantis to help fully charge the station’s tanks. While the IVA team had worked in the tanks and Sullivan had stood by to come for assistance, the rest of the crew had worked in Atlantis to prepare for consumables transfer over the coming days.



On July 15th, NASA granted STS-38R a day of relative rest for Flight Day 6. The major activities of the mission lay behind them: the crew now had free run of Atlantis, her Spacelab cargo, the ET-007 tubes, the PCAM passage, the mid-deck and orbital operations center of Enterprise, and the LLM and airlock in OV-101’s payload bay. The day was spent in organizational tasks and cargo transfer, with the crew forming a “bucket brigade” to fling cargo bags and air canisters around the tight corners of the ET-007 access tubes where the day before Garriott and Thuot had struggled in their suits through the constrained manholes into the tanks. With the major work to activate the station complete, the time constraints on the STS-38R fell away. Over Flight Days 7, 8, and 9, the crew were able to gradually complete the process of unloading their cargo, stocking the station’s larders, then setting the station into a quiescent mode to wait out the time until its next visitors. As Atlantis drew away from the station on Flight Day 10, the crew was granted perspective on their accomplishments of the last week. The station now spread its massive solar wings and looked ready and waiting for the next crew. Enterprise’ STS-37R launch had been a massive risk for an agency still smarting from the loss of Discovery, but STS-38R’s experienced hands and capable rookies had made good on the wager.

The final statistics of Space Station Enterprise following the STS-38R deployment mission were staggering. Even discounting some of the primary structure of OV-101 and other systems only needed for launch, Enterprise’s single launch had carried more than 150,000 kilograms of useful payload to orbit, more than ten times that of typical Space Shuttle missions. The core modules of the station (OV-101 crew module, Leonardo Lab Module, airlock, and intertank tunnels) constituted two hundred cubic meters, already larger than the Soviet Mir, and had proven easily capable of supporting the visiting crew of seven from STS-38R. The LOX tank added another six hundred cubic meters, and when outfitted would eventually bring the station up to nearly three times the size of the Skylab station which had preceded it, though that would have to wait many more missions. The staggering volume of the fifteen hundred cubic meter liquid hydrogen tank remained a dream for another day, one which would once again nearly triple the size of the station. Even American planners still struggled with how to effectively convert such a large volume on orbit for operational use, and with how many crew such a large volume might require or justify.

With STS-38R concluded by Atlantis’ landing in Florida, the flags for both Enterprise and Atlantis were moved. Atlantis’ flag would continue to follow the orbiter as she made her way to the OPF to prepare for her next flight. Enterprise’ flag was moved to fly just outside the Launch Control Center, marking the orbiter’s continuing flight. To many on the ground, STS-37R and STS-38R solidified the new era in the space program: a dramatic accomplishment that pad workers and support teams could look to as a model of what could go right after Discovery’s loss. Enterprise was a model for what the program could aspire to as it moved on from the tragedy. In the future, the Enterprise flag would roll to the pad with each new mission to support the station, flying just below the orbiter’s own flag. However, while Enterprise waited on its next crew, the future of American spaceflight was being radically reshaped in a way inspired by Enterprises fantastically successful launch.



Artwork by: @nixonshead (AEB Digital on Twitter)

 

[TimothyC]

Boldly Going Part 10



Only hours after Atlantis landed in Florida, President George H.W. Bush made a speech from the steps of the National Air and Space Museum in Washington D.C. Along with Administrator Truly, he marked the 20th anniversary of the Apollo 11 moon landing in a grand fashion, marking not only the recent successes of the Space Shuttle and Space Station programs, but also laying out a plan for the future: a future which would exploit the success of Space Station Enterprise while also laying the groundwork for a return to the moon and a path onward to Mars.

In 1961 it took a crisis -- the space race -- to speed things up. Today we don't have a crisis; we have an opportunity. To seize this opportunity, I'm not proposing a 10-year plan like Apollo; I'm proposing a long-range, continuing commitment. Already, in the next few years: Space Station Enterprise, our critical next step in all our space endeavors. And next, beginning in the coming decade, the 1990s: Back to the Moon; back to the future. And this time, back to stay. And then, in the new century, a journey into tomorrow, a journey to another planet: a manned mission to Mars.

Each mission should and will lay the groundwork for the next. And the pathway to the stars begins, as it did 20 years ago, with you, the American people. And it continues just up the street there, to the United States Congress, where the future of the space station and our future as a spacefaring nation will be decided.

And, yes, we're at a crossroads. Hard decisions must be made now as we prepare to enter the next century. As William Jennings Bryan said, just before the last turn of the century: “Destiny is not a matter of chance; it is a matter of choice. It is not a thing to be waited for; it is a thing to be achieved.''

And to those who may shirk from the challenges ahead, or who doubt our chances of success, let me say this: To this day, the only footprints on the Moon are American footprints. The only flag on the Moon is an American flag. And the know-how that accomplished these feats is American know-how. What Americans dream, Americans can do. And 10 years from now, on the 30th anniversary of this extraordinary and astonishing flight, the way to honor the Apollo astronauts is not by calling them back to Washington for another round of tributes. It is to have Space Station Enterprise up there, operational, and underway, a new bridge between the worlds and an investment in the growth, prosperity, and technological superiority of our nation. And the space station will also serve as a stepping stone to the most important planet in the solar system: planet Earth.

As I said in Europe just a few days ago, environmental destruction knows no borders. A major national and international initiative is needed to seek new solutions for ozone depletion and global warming and acid rain. And this initiative, “Mission to Planet Earth,”' is a critical part of our space program. And it reminds us of what the astronauts remember as the most stirring sight of all. It wasn't the Moon or the stars, as I remember. It was the Earth -- tiny, fragile, precious, blue orb -- rising above the arid desert of Tranquility Base.

The space station is a first and necessary step for sustained manned exploration, one whose critical beginning we’re pleased to celebrate. To strike forth along the path already blazed by the brave crew of Atlantis, today I'm asking my right-hand man, our able Vice President, Dan Quayle, to lead the National Space Council in determining specifically what's needed for the next round of exploration: the necessary money, manpower, and materials; the feasibility of further international cooperation; and develop realistic timetables -- milestones -- along the way. The Space Council will report back to me as soon as possible with concrete recommendations to chart a new and continuing course to the Moon and Mars and beyond.

In the wake of the President’s speech, Vice President Dan Quayle and the National Space Council worked with NASA on the challenge they had been set: develop a plan for a bold new future for NASA, one which would draw on the agency’s existing accomplishments while living up to the legacy of their previous successes [1]. The next three months would be consumed by what was unsurprisingly referred to as the “90-day study,” which would lay out the groundwork of options which would be presented to Congress for further input. The main challenges the study had to address were three fold. First, how could the existing success in launching Space Station Enterprise be exploited, in line with existing plans for international cooperation on the station’s growth and development. Second, how could that international cooperation and the success of the Shuttle’s legacy to date be exploited for the challenge of a return to the moon and eventually for exploration beyond. Third, what budget would be required, and how the program could be conducted in a way which Congress would find acceptable and worth funding less than a year after the Shuttle’s Return to Flight.

In this, Space Station Enterprise would provide not only a critical technical stepping stone, but also a programmatic model. In its original form, Reagan’s selection of Space Station Enterprise had short-circuited many NASA internal space station development programs. The selection of a program directly derived from legacy hardware had been initially seen as a gamble, one NASA had not preferred from among the options presented to the President. In the program’s difficult early years between detailed design and hardware fabrication, the entire agency had struggled with the true scope of hardware modifications required. Many had doubted if the station was truly going to be any more capable or better than the dedicated space stations it had inexorably sidelined. Moreover, in the wake of Discovery’s tragic loss, some had wondered if Space Station Enterprise itself represented an unacceptable risk in the pursuit of an unrealistic timetable for a new American space station. However, Enterprise was a risk that had paid off. Now, it remained to plan for a future building upon its success.



Images from @nixonshead (AEB Digtial on Twitter) & George H.W. Bush Presidential Library

[1] Less of this speech is changed than you might think. See the full text here: https://web.archive.org/web/2011060...ry.tamu.edu/research/public_papers.php?id=712

 

[e of pi]

Boldly Going Part 11

During her launch, Enterprise had carried a level of payload never imagined for the Space Shuttle. In a certain sense, the 150 metric ton payload of Enterprise on STS-37R exceeded the maximum ever achieved by the mighty Saturn V--a rocket well and truly demonstrated capable of the lunar mission, and widely baselined for NASA’s internal Mars studies in the 1960s and 70s. Moreover, whatever the worries about risks and delays before launch, the station had successfully flown just weeks before the National Space Council gathered to begin work on their 90-day study. As they started, Space Station Enterprise was now orbiting overhead waiting to be exploited, turned into a space station larger than almost any NASA had dared to dream of...and several years before those other studies could have been imagined to have flown. In laying out their analysis for the 90-day study, Administrator Truly and Vice President Quayle would try to seek similar areas where the success of the program could be ensured by seeking lower cost, lower complexity solutions. Enterprise provided an example of how, through careful selection, such solutions - though perhaps less optimal than a clean sheet design - could nevertheless meet the agency's needs. As NASA struggled to conceive a plan which could achieve ambitious goals for the future on a limited budget, such minimization of complexity in the near term could help ensure the success of ambitions for the future: the full conversion of Enterprise into a permanently-crewed outpost, beginning a lunar program with the aim to place the United States and any willing allies back on the path to the moon within the 1990s, and finally laying the groundwork to allow a future program for Mars.

Enterprise’s success from aiming for the near and medium-term and allowing long-term plans to be developed and executed more fluidly in response to developments would provide a model for handling Mars: no concrete budget or schedule deadlines would be provided. Instead, goals and technologies for the program would be allowed to flow from successes encountered or hardware developed in lunar planning. Thus, the full options presented to Congress with cost and schedule projections would focus on the first two areas: the station and the moon. To meet the goals for space station operations and lunar explorations, NASA again drew on the experience of Enterprise to win approval for a program Congress might not have been willing to approve if not couched as a fallback option. Instead of a single monolithic plan, NASA presented several options varying in level of funding, schedule, and architecture. It would fall to Congress to select from among these recommendations.

The state of Space Station Enterprise planning before Bush’s “Space Exploration Initiative” bears some review. At the start of the project in 1983, Enterprise had been intended as a limited-duration expedient. While international partners like ESA were involved from the start, initially plans for broader involvement by ESA and the Japanese human spaceflight agency NASDA (later merged into JAXA) were focused on successor stations, more like the originally considered “Space Station Freedom” concepts: large, multipurpose, multi-module stations which would be centers of orbital operations and infrastructure. As the Space Shuttle program had ramped up and Space Station Enterprise itself had proved more challenging than expected, it had gradually become clear that SSE itself was shutting out such stations from existing on schedule. By 1986, ESA and NASDA realized that if they wanted to work with the Americans on a large station program, it would have to be with the expansion of Enterprise. Thus, though the hardware for Enterprise’s core modules saw little change even as their launch date slipped by two years, the period between the loss of Discovery and Enterprise’s launch in 1989 saw NASA and its international partners working out preliminary concepts for expanding the station to fill much of the role the Space Operations Center-style Freedom had originally been conceived to address.

While Enterprise’s LOX tank volume of 560 cubic meters made habitat space readily available, Enterprise’s laboratory capacity was more limited. Only Spacelab Instrument Rack drawers could be transferred into the station, around the intertank passages, and on through the mid-deck of OV-101 to the Leonardo Laboratory Module (LLM). Larger installations like the proposed “International Standard Payload Rack” (ISPR) could not be moved given the small hatches subdividing the station. Additionally, the station had only two ports for visiting vehicles and future expansion. The international partners and NASA had come to rough agreement on methods for solving these issues: ESA and Japan would both be able to launch laboratory modules aboard the Space Transportation System and the crew to serve them, in exchange for providing hardware which would contribute to the station’s capabilities and expansion. NASA, for their part, would provide a LOX tank fully outfitted as a habitat, with internal partitions, hygiene systems, and the life support equipment for the station as a whole. However, given the 36” diameter hatch into the LOX tank, the ability to use the LOX tank as laboratory space would necessarily be limited to Spacelab-standard drawer modules. Thus, they would become a defacto standard for the many pieces of modular equipment the LOX tank would house, as they already were in the existing Leonardo laboratory. However, the experiments which could be housed in such SIR drawers were relatively rudimentary compared to the larger mass and volume available to ISPR-mounted experiments. Only the newer modules would be capable of both housing such racks and moving them through the new, larger vestibule hatches to or from other modules or visiting vehicles. Japan was tentatively agreed to be providing the two node modules which would provide the space for the station’s expansion. Most critically, in the wake of the extended stand-down of the Space Shuttles following Discovery’s loss, ESA would provide the on-orbit crew lifeboat which would ensure any astronauts on the station or a visiting Space Shuttle crew would always have a ride home in the event of further issues with the Space Shuttle.

These plans were fairly advanced by 1989 and had developed significant support within both American and international agencies and governing bodies. It was anticipated that only the station core’s launch delayed formal support from the White House. ESA had gone so far as to shape decisions about their independent human spaceflight plans around Enterprise requirements. In order to be ready for a role as a space station lifeboat. After extended and contentious debate, ESA had decided against the French “Hermes” spaceplane proposal as their primary crew vehicle. Instead,in 1987 they had selected an Italian design for a “Multi-Role Recovery Capsule,” based heavily on the British “Multi-Role Recovery Capsule” proposal of the same name. The capsule was anticipated to serve as a “cheap and cheerful” solution to the combined mission of an Enterprise lifeboat and independent crew vehicle capable of launching on their existing Ariane 44L lifter. In a sop to French pride wounded by selecting an Italian implementation of a British concept over the wishes of the French space agency, CNES, France was approved to build both the new Ariane 5 launch vehicle and a logistics vehicle capable of fully utilizing it, and would also supply the thermal protection system for the new MRRC. While ESA would have preferred to have both the capsule and the more ambitious spaceplane, the switch to the less ambitious capsule as the sole crew vehicle for Europe would reduce costs and free up budget for the assumed-imminent Enterprise laboratory modules. Japan was likewise conducting advanced studies on their planned laboratory module. Thus, even by 1989 international partners had begun to shape their future space programs around assumptions for Space Station Enterprise’s utilization and growth. Bush’s refocus of NASA’s priorities on the moon threw these plans into jeopardy and led to massive international confusion.





Artwork by: @nixonshead (AEB Digital on Twitter)

 

[TimothyC]

Boldly Going Part 12

President Bush’s Space Exploration Initiative brought with it a new focus on a lunar mission to join NASA’s existing Space Shuttle and Space Station Enterprise programs. With this new objective came questions about how the priority of existing projects might change. Was Enterprise to be left largely behind, diminished to nothing but a waystation for extended Space Shuttle missions? Or was it to be radically retooled, converting the hydrogen tank to full use as well, with a crew of a dozen or more, with European and Japanese participation rendered far less important and perhaps undesired? Proposals, schedules, and budgets along all three lines were considered by the 90-day study team, and their final recommendations formalized these three paths as Option A, Option B, and Options C. Option A was “crew-tended” basic utilization, with no permanent crew, only limited outfitting of the oxygen tank volume, and only a single additional node for visiting Space Shuttles and temporary scientific or logistics modules. Option A would still radically increase Shuttle capabilities, potentially tripling mission durations by running almost all Shuttle power from the station’s 25 kW continuous power supply. This would allow missions to Enterprise to keep crew on orbit for nearly a month at a time. Even as few as six such missions a year could see Enterprise spend almost two-fifths of the year “crew-tended” even with no permanent staff. Experiments could remain on station during the roughly one-month gaps between missions, offering a smooth transition from short-duration Shuttle flights to long-duration Enterprise-augmented missions to stays on orbit measured in months or years, all using the Spacelab Instrument Rack drawer standard. Engineering and launch of all Option A elements was estimated to be possible entirely from American internal resources by 1994, for less than a billion dollar increase in spending beyond the existing Enterprise launch and a $10 billion dollar total program cost for a decade of operations.

Option B would consist of plans along the lines already existing, adding additional solar power generation, Japanese and European labs, the European-built Multi-Role Recovery Capsule (under American terminology, serving as the “Assured Crew Return Vehicle”) and a permanent crew numbering between 6 and 12. It could reach initial operational capacity before the new millenium and perhaps several years sooner, depending on budget profile, but would require a minimum budget of tens of billions in additional research and development. The cost for Option B to even reach full operational configuration was more than Option A required for a decade of service. Over a fifteen year program, Option B would commit NASA to total station expenses (both development and ongoing) of perhaps $40 billion even as they moved forward with lunar and (in the new millenium) Mars planning which would no doubt be hungry for funding.

Option C was the most ambitious, adding several new American lab modules and habitat space for at least a dozen crewmembers as the core for a massively expanded station. The additional crew could be kept busy within hangars which would offer servicing for orbital transfer vehicles for operations around cislunar space, places to repair and refit satellites, and act as berths to assemble and check-out large Mars-bound crewed spacecraft. However, the budget for this would be the most extreme, running to several billion dollars per year with a completion date stretching beyond 2001. Supporting the resulting $150+ billion two-decade-long station program was realistic only if the most optimistic of the 90-day Study’s overall budget profiles was pursued, with multi-billion-dollar increases in the agency’s budget for low-Earth orbit operations alone to avoid cuts in funding of uncrewed exploration, space telescopes, aeronautics research, and perhaps even lunar exploration to pay for such an exorbitant spacecraft.

For the moon, the study developed similar tiers for Congress to consider for selection, Options D, E, and F. For simplicity of explaining the options to Congress and the public, the names for the options were aligned for expansion into descriptions of their intentions. The low-end lunar mission, Option E, was also referred to as “Early Lunar Access” or ELA. ELA consisted of the assembly of two components, each launched by the existing Titan IV and Space Shuttle vehicles, to make for a single small lander. This human landing system would have a cargo capacity sufficient only for either landing two crew on the surface with propellant to return to Earth or sending a payload of 8.5 metric tons on a one-way flight to the moon. Three such landers would land the crew, a tiny habitat module, and a relatively large stationary science array to support roughly two weeks of intensive exploration of the surface. While capable and requiring no new launch vehicle development, this would require six launches and three orbital assembly missions. Though capability could be expanded by landing additional consumables, adding additional crew and growing to a full lunar outpost with derivatives of the system would be essentially impossible given likely launch rates and flight cost. Option E was fast and cheap to develop, running perhaps less than $10 billion, but would yield little more than flags-and-footprints. Worse, the individual missions would require half a dozen large rockets, resulting in an astronomical per-flight cost running as much as $2 billion.

By contrast, Option F represented a wish list unseen since the Integrated Program Plan or Apollo Applications Program. Also called the “First Lunar Outpost” (FLO), Option F would depend on a massive lander capable of delivering dozens of tons of payload to the lunar surface, landing crews of four to six for missions lasting weeks in a single event. This would be enabled by the development of the “Magnum” launcher concept. Magnum was the maximum growth limit of Shuttle-derived future launchers, adding multiple liquid boosters each larger than the existing SRBs on an inline launcher, resulting in more than 200 metric tons of payload to initial Earth parking orbit. A single such mission would exceed the entire scope of the Apollo program's science capability and multiple landers accumulating their payload in one spot would rapidly grow into the aspirational outpost. However, while operational missions could be relatively low-cost for their payload (given they used only one heavy lifter), the upfront development time and cost was exorbitant, running to as much as $40 billion [1] for the complete program through the first landing and initial outpost operations.

Option D had been given the internal name of the “Design Reference Mission,” a basic mission plan from which the other missions could be baselined and to which they could be compared. Drawing inspiration from the Space Station Enterprise launch, this Design Reference Mission would use a sidemount lifter derived directly from existing external tank and SRB hardware for its early launches, with the potential for a growth option using liquid rocket boosters later. This would allow launch vehicle demonstration flights only a year or so behind ELA’s aggressive schedule, with two or three of the relatively low-cost Shuttle-C missions combining to have enough capability to compare well with the FLO option. Though development might cost as much as $20 billion, operational flight costs would be comparable to ELA’s multi-launch missions while being both simpler and more capable. Congress received the 90-day study report on November 20, 1989, and immediately the top-line figures resulted in screeches. If both maximum options were combined, then the next decade and a half of NASA operations could run to more than $200 billion. By contrast, the two least expensive options would combine to a budget of “only” an additional $20 billion, but would amount to abandoning the plans for Space Station Enterprise, throwing away the station NASA had assured Congress they needed for a decade in pursuit of the next shiny objective.

The point could not be avoided that in almost any case the station program would represent a massive fraction of the combined Space Exploration Initiative program budget, unless Option A’s minimal crew-tended station was selected. Even Option B’s concept to execute the planned agreements with Europe and Japan for station expansion paired with the most exhaustive Option F lunar outposts would result in nearly 40% of the combined budget being spent on station expansion and operations even as the remainder executed a major lunar exploration program. Though Congress grumbled about formally authorizing the expenditures for the Option B expansion of Space Station Enterprise, the station had been the program of record for NASA for almost 8 years and the growth plans had been gathering their own inertia inside NASA and on the Hill for at least two years. With NASA’s success launching the station so fresh in everyone’s mind, few in Congress were willing to effectively cancel its utilization.

While Option B was becoming the front-runner for station development, the President’s signature lunar objectives were finding a frostier reception. Democrats in Congress questioned the need for spending perhaps as much as $70 billion dollars on Option F for the establishment of an off-world outpost. The lower-cost Option E was criticized for the level of spending required for execution of any real development and that in spite of being supposedly “Early Lunar Access,” it would reach the lunar surface only a few years sooner than the Design Reference Mission. Additionally, for all the President’s high-minded statements about lunar science and the exploration and development of the lunar surface for the good of humankind, Option E’s ELA system would be severely limited in its exploration capability. With the fate of the lunar program uncertain, Congressional approval of both the lunar and station programs was delayed well into the new year, though limited budget increases were approved for Space Station Enterprise operations and further studies on all options.

ELA painting from "GD Goal: Low-Cost Manned Lunar Missions", AvWeek Jan. 18, 1993




Renders done by JFA for NASA on First Lunar Outpost:


https://spaceflight.nasa.gov/gallery/images/exploration/lunarexploration/html/s92_38477.html


https://spaceflight.nasa.gov/gallery/images/exploration/lunarexploration/html/s92_38479.html


https://spaceflight.nasa.gov/gallery/images/exploration/lunarexploration/html/s92_38475.html


https://spaceflight.nasa.gov/gallery/images/exploration/lunarexploration/html/s92_38476.html

[1] Higher and more realistic than OTL's optimistic project of an HLV for $5 billion, and an entire program through first landing of ~$25 billion From the National Space Society page on the First Lunar Outpost concept.

Edit note: the original version of this post had much larger images inline. I changed that when I realized that these five images total 54 megs, and I didn't want to think of what that was doing to my server. The images themselves are links to the full versions.

 

[e of pi]

Boldly Going Part 13

Congressional debate on the fate of Bush’s 90-day Study exploration programs delayed the higher direction of the space program through the end of 1989 and well into 1990. In the meantime, though, NASA and international agencies were not standing still. As Congress weighed their response to Bush’s challenge and the arc of the next decade or more of exploration, Space Station Enterprise still awaited its next crew. Indeed, the Space Shuttle had continued its return to operations even before the 90-Day Study report was issued. Space Shuttle Columbia launched for the STS-39R mission November 17th, 1989--just three days before the report’s release. Carrying a classified Department of Defense payload bound for a near-geosynchronous orbit, STS-39R marked some of the new pattern of Space Shuttle operations: any mission which could travel to the station’s 39-degree orbit would do so, even if the station’s mission-extention or scientific capabilities were not specifically required, ensuring the capability of a “safe-harbor” abort-to-station to await Launch-on-Need support if the orbiter could not be cleared as safe for return. As with previous contingencies, though Atlantis waited on the ground with the launch-on-need stack, Columbia proved not to require it. The payload, speculated to be a “Magnum” intelligence satellite, was deployed with its Inertial Upper Stage and made its way to geostationary orbit, and Columbia returned safely through entry. The quick turnaround of Atlantis was mandated by the decision to send Challenger in for her Orbiter Maintenance Down Period (OMDP). With Challenger off the flight rotation following STS-36R, Atlantis and Columbia would have to shoulder the load alone until her return--a fact which emphasized NASA’s request in every case of the 90-Day Study for the construction of a new orbiter from structural spares already ordered to bring the fleet back to four operational vehicles. This would ensure that even with an orbiter in for the long-duration OMDP, there would still be available three flying orbiters: one vehicle in preparation for launch, another nearing flight-readiness for Launch-on-Need duty, and the third earlier in the processing flow. This would cut the time between missions by half, enabling flights every 2 to 3 months instead of every 4 to 5.

While Congress chewed over the 90-Day Study Report’s options, the flag of Space Station Enterprise once again made its way to the pad at Kennedy Space Center, this time flying below that for Atlantis as that orbiter prepared for the first operational flight intended to visit the station. In many respects, STS-40R was tasked with a mission like almost all space station missions envisioned by Option A. Atlantis flew to orbit carrying a Spacelab module. Once it reached the station on Flight Day 2, Atlantis docked to Enterprise and connected its power systems to the station, allowing Atlantis to draw on the power of Enterprise’s large solar arrays. With the resulting lower consumable consumption, Atlantis stretched the record for space shuttle missions. The 8 crew aboard the orbiter had 16 days on orbit to work on the experiments they brought with them, including transferring some into open rack drawers in the station’s Leonardo Lab Module for longer duration untended operations. By using the sleep stations aboard Enterprise in addition to those carried about Atlantis’s mid-deck, every member of the crew had their own private space for rest and recreation and the additional “space toilet” was noted to avoid certain bottlenecks in crew operational rhythms. As a result, crew morale remained high in spite of the longer mission duration.



Atlantis’s STS-40R mission would prove a model for future Space Shuttle missions, which would continue to push the envelope of the orbiter’s duration on-station and the crew which could be launched aboard one flight given the ability to roughly double the support and habitat facilities once docked to Enterprise. While congressional deliberations over whether NASA would return to the moon and if anything more than “Option A” would be approved as a future for the station proceeded during 1990, NASA launched Columbia on STS-41R in a satellite deployment mission similar to STS-39R. Late in the summer of 1990, Challenger returned from her OMDP to return the Shuttle Program to Vandenberg operations with STS-42R. The polar orbit required for the mission proved a challenge: the orbiter would be unable to “abort-to-station” given the inclination differences. With only one orbiter pad available at Vandenberg, preparations for the Launch-on-Need mission proved complicated. In order to reach Challenger, Atlantis would have been forced to make her flight to polar orbit from KSC. Individual variation in hardware and trajectory for STS-42R’s support mission was complex enough that it spurred a change in the mission numbers for Launch-on-Need missions, given the extensive analysis and planning required and its deviation from previous Launch-on-Need missions. Instead of the “STS-300” designation handed from one orbiter to the next for the previous four Launch-on-Need support missions, Atlantis’s support task was designated as STS-343, matching the STS-43R mission the stack would fly if the precaution proved once again unnecessary. If flown, STS-343 would have required a dogleg north over the Carolinas once the SRBs were dropped, overflying the continental US as far as Cleveland. The delta-v penalty resulting from this trajectory was enough to reduce the orbiter’s payload to only 6,000 lbs, though the unconventional ground track at least ensured several downrange abort options throughout the trajectory. While entirely unsuited for operational missions, this payload was sufficient for the Launch-on-Need mission requirement. Though unflown, the analysis for Columbia’s STS-343 contingency would prove the model for Launch-on-Need support for remaining Vandenberg flights [1]. This allowed the Space Shuttle to fly out missions like Keyhole which otherwise would have had to be switched to the Titan IV rocket at great expense in replanning and lower-priority missions which might have simply been cancelled unflown.



Throughout 1990, the Space Shuttle was seeking a new normal in flight operations, both beginning operations at Space Station Enterprise and working to clear the backlog of missions waiting since the loss of Discovery. However, activity on Capitol Hill was slower. More than a year after the original presentation of the 90-Day Study report, Congressional action implementing any of the options for the President’s vision was still lacking. Congress was still delaying formal authorization of any of the options for lunar and station operations while it awaited the results of more detailed studies of the implementation of “Option B” for station expansion and the three lunar options which had been funded for fiscal year 1990. The absence of action following the President’s directives stressed NASA and drove international partners to distress. Both ESA and Japan’s NASDA had anticipated signing memoranda of understanding on the long-planned international expansions to Enterprise more than a year prior, in ESA’s case over substantial internal debate resulting from intra-agency conflict between national space agencies over ESA’s direction.

France in particular had complained vigorously over the “American hegemony” of ESA’s program direction, still smarting from the selection of the less-ambitious Italian/British Multi-Role Recovery Capsule over the more capable French spaceplane concept. Given the delays to international participation in Space Station Enterprise and the serious consideration of the idea of cutting off all international participation entirely with NASA’s “Option A’ station, France saw an attempt to head off any independent European program which might launch something like the Columbus Man-tended Free Flyer laboratory station to equal the capabilities of Enterprise the same way the MRRC lifeboat had eclipsed the chance for a European Shuttle alternative. If ESA as a whole would not take action, then France would do so alone. Late in 1990, the French space agency CNES signed a memorandum of understanding with the cash-strapped Soviet Union to launch French astronauts to the Soviet Mir space station, including outfitting one of the remaining laboratories to include some CNES experiments. This visible break from ESA’s general program direction was embarrassing to ESA, NASA, and even the Japanese, who now looked as though they were in fact awaiting American instructions for their own program. However, the American agency was able to use it as an example of the urgency of providing a clear direction for their development, providing some of the final advocacy to get NASA’s new authorization act finally approved early in 1991.

Artwork by: @nixonshead (AEB Digital on Twitter)

[1] Polar launches out of KSC were developed historically as a part of the HEXAGON (KH-9) retrieval mission, if such a flight was desired prior to SLC-6 being activated, which is the origin of this trajectory diagram: https://www.nro.gov/Portals/65/documents/foia/declass/FOIA for All - Releases/F-2017-00070d.pdf

 

[TimothyC]

Boldly Going Part 14

After all the debate, the plan for NASA as approved in 1991 was, quite simply, right down the middle. As expected, “Option B” was selected for expansion of Space Station Enterprise. ESA and NASDA each signed a memorandum of understanding with NASA to formalize their participation later that year. ESA would provide their MRRC as a crew lifeboat and alternate crew access vehicle in exchange for launch of a laboratory module and crew slots aboard station, while Japan would provide the hulls for the two node modules in exchange for the launch of their own lab and crew. After a delay of nearly 2 years, Bush finally saw Space Station Enterprise’s expansion back on track. However, the biggest headline was the formal blessing of NASA’s new lunar ambitions. The new program, formalized as the “Minerva Program,” was approved and budgeted for full design studies and development. The project would follow roughly along the lines of NASA’s baseline Option D Design Reference Mission, and the new program office began issuing contracts almost as soon as it came into formal existence. Marshall would coordinate the development of the Shuttle-C cargo launch vehicle, building on Enterprise experience, while Johnson would coordinate the human landing system. Other centers like JPL, Lewis, and Ames would develop surface hardware and robotic precursor missions. Much like Reagan’s goal to launch Enterprise “before my term is up,” the goal of launching the first Minerva crew to the moon within the decade was unofficial, but widely understood to lurk behind a planning date which settled neatly into 1998.

Development of the Shuttle-C vehicle was anticipated to be the simplest aspect of the program, given the recent launch of Enterprise as a “cargo launch vehicle” pathfinder. However, it was quickly complicated by other factors. The inability to return Enterprise’s three RS-25 Space Shuttle Main Engines to the ground had long been a sore point, and the lunar program’s expected need for two to six Shuttle-C flights per year would stress production of even a cost-reduced RS-25. Thus, the design for Shuttle-C evolved to include a reusable boat-tail, incorporating the three SSMEs and the vehicle’s avionics into a single package capable of diving through the atmosphere nose-first and surviving for recovery via a parachute post flight. Though more complicated than simply excising the propulsion boat-tail from the orbiter design and building a cost-reduced expendable copy, the development of this reusable propulsion and avionics module was anticipated to substantially reduce operational costs for the lunar program. Still, once the first major dam had burst, further changes came quickly.

The orbital propulsion and avionics module quickly became a platform for implementing other Space Shuttle “wishlist” items like the replacement of the Auxiliary Power Unit generators and hydraulics with a new system for gimbaling the three engines and aerodynamic surfaces using electro-mechanical actuators (EMAs). This would eliminate two fluid handling systems from the vehicle, making it substantially easier to service. A similar system had long been desired for the orbiter fleet, and indeed its addition to Enterprise had been studied during the station’s conversion with the goal of eliminating the need to launch an orbiter’s APUs for a mere eight minutes of operation. While introducing it to the orbiter fleet in the mid-80s had been a step too far, now they found their home on the two initially-ordered vehicles. Similar stories occurred throughout the detailed design of the stack, with the result that the program rapidly grew in both cost and schedule. A prime example of this was the decision to replace the Shuttle-C’s solid rocket boosters (as used on Enterprise and every other Space Shuttle launch) with new liquid rocket boosters. Serious issues with the solid rocket boosters had been found during the post-Discovery investigations, requiring the rapid implementation of plans to make the joints between the solid segments safer. However, the cost savings of reusing the solid rocket boosters had largely not turned up. The challenges of retrieving boosters from the sea, breaking them down and shipping them back to Utah for refilling, then returning them to Florida and restacking into integrated boosters left the costs of the refurbishment similar to simply manufacturing new booster casings. Liquid rocket boosters, particularly if their engines could be reused with the relatively cheap tanks expended, offered a chance not only to increase Shuttle-C’s performance but to do so while decreasing operational expense. While approved for Shuttle-C, there was hope of applying these changes over time to the main Space Shuttle program as well.

Many of these changes originated within Marshall, which formally directed the program, but given Shuttle-C’s formal subordination to Minerva’s budget line, all such changes also had to touch the desk of the new Associate Administrator for Exploration, Mike Griffin. Griffin had long had the personal belief that the loss of the Saturn V had been a tremendous setback for NASA, and had personally supported the Option F program and its larger-capability, Saturn V-equivalent, Shuttle-Derived Heavy Launch Vehicle (SDHLV). When taking over his new role overseeing Minerva in 1991, he was stuck with the size category which had been approved, but was determined to see it be as technologically advanced and operationally effective as possible to increase the odds of being able to apply it to programs outside of “just” Minerva. Griffin’s influence was key to the approval of many of the largest changes which would come to define Shuttle-C, including the liquid rocket boosters and the reusable Orbital Propulsion and Avionics Module. The politicking required for Griffin and Marshall to get their way on this scope creep meant delays both to approval and to availability of the final product. However, they argued successfully that with the clean-sheet lander as the primary pacing item, Shuttle-C had development time to burn. By the end of 1991, the design process for Shuttle-C was well underway. Marshall had issued contracts for all the major subsystems of the rocket: the Orbital Propulsion and Avionics Module (to Rockwell), the Payload Fairing (to Martin Marietta), the new Liquid Rocket Boosters (to General Dynamics), and the Exploration Upper Stage (to Boeing) which would finish the system’s job by injecting payloads to the moon and beyond.

While the new components of Shuttle-C proceeded into detailed design at Marshall, the Minerva team at Johnson focused on the conceptual details of the new lander design.The rough scope of the lander program was set by the selection of the launch vehicle and the missions NASA expected the vehicle to perform. The requirements NASA set out for their internal design teams and industry study partners to fulfill with the new “Lunar Surface Access Module” (LSAM) called for a lander which could be prepared for a lunar cargo or crew flight in just two launches of the Shuttle-C. Subtracting mass reserved for a lightweight crew return capsule, this would require a mass of no more than 40 metric tons fully outfitted for crew launch configurations and 42 metric tons for cargo-delivery missions. Within this the LSAM would have to fit the ascent and descent stages, the crew’s surface habitat, and the consumables to support a crew on the lunar surface for a reasonable time. NASA studies for Options D and E had analyzed the performance of the Apollo crews, and discussed in some detail the balance between a larger crew and a smaller crew staying for longer times. After all, the two-person crews of Apollo had performed admirably in all major mission tasks, including troubleshooting vehicles on the fly and carrying out surface science. Adding an additional crew member to the landing party required at least 200 kg of astronaut and support systems (such as an additional EVA suit). Expressed instead as additional consumables, even 200 kg was enough to double or triple the surface stay for a crew of two, while providing more gear to enhance their productivity. The loss from a smaller crew came mostly from the loss of redundancy in the event of an astronaut being injured during the mission and in the loss of specialization. Either selenologists and physicists would have to train sufficiently to take over systems engineering roles during descent as had Harrison Schmidt on Apollo 17, or the entire surface science capability of early sorties would depend on the training of pilot-turned-selenologists. Whether Minerva accepted missions little longer than Apollo but with twice as many crew or missions several times longer but with only the same crew capacity as Apollo, the lander would be a formidable science vehicle even for short sortie missions.

For plans further in the future, the capabilities of the vehicle would also have to be driven by the requirement to land a large emplaced habitat and other heavy hardware to support the development of a lunar base which the President and Congress had tentatively authorized, and which NASA hoped would materialize in truth. By using an additional two Shuttle-C launches, a second lander could carry almost 15 metric tons of cargo to the lunar surface. This was enough that a crew lander groaning under the requirements of landing at least four astronauts to the surface and returning them to space could be allowed to carry minimal other cargo, while still supporting a stay measured in weeks or months. Only a few such landings at the same site would rapidly build up the infrastructure of a permanent base to rival the capabilities of Space Station Enterprise in low Earth orbit. However, the challenges of designing the vehicle for crew and cargo delivery were non-trivial. The Shuttle-C payload shroud was cavernous, with axial height to spare. However, the height of the vehicle above the ground was a consideration for astronaut safety when alighting from the vehicle’s deck, and every meter above the surface complicated the task of moving massive cargo modules from the deck of a lander to the surface. In considering the award of the lander prime contract, NASA searched for ways to maximize the potential of the lander as a base-building element in ways which wouldn’t jeopardize the capabilities as a sortie vehicle. When Johnson awarded the contract for the new LSAM to McDonnell-Douglas in November 1991, it was at least partly due to their eager embrace of a unique concept which had emerged from Johnson’s teams in NASA “blue-sky” lander plans.

While the majority of NASA’s attention was drawn by the return to the moon, the Space Station Enterprise Program Office wrestled with suddenly being forced to execute what they had been dreaming about for years while being a distinct second in terms of internal priority. Officially, President Bush had identified the expansion of Space Station Enterprise into a fully crew-rated, permanently-occupied station as the immediate priority for NASA in the coming years. However, in practice the agency’s attention and that of their contractors and the general public was drawn like a moth to the more exciting prospect of a return to the moon. While authorized for the “Option B” permanently occupied station with expanded habitat and lab spaces, for the moment Enterprise was stuck as something quite similar to “Option A”--a work site which could temporarily house Shuttle crews during extended missions and which could host crew-tended experiments between Shuttle flights. Bridging the gap from one to the other while negotiating international diplomacy, standardization of systems designs across multi-national development teams, and the ongoing challenges of continuing to convert a Space Shuttle into an operational Space Station were anything but trivial. However, these challenges were difficult to convey to the public. The need to deploy the station’s massive solar arrays to allow it to survive had made for dramatic television during Atlantis’ STS-38R mission, but in order to power added labs and habitat spaces, new and larger panels would need to be added to augment the generation capability. The new International Standard Payload Rack had to be designed for the larger experiments to be installed in the Japanese and European lab modules, as well as the logistics modules for Shuttle to carry them to and from the station. At the same time, plans had to be fashioned to adapt the anti-slosh baffles into the LOX tank to the Spacelab Instrument Rack drawer which would be the standard equipment unit for life support systems, exercise gear, living, and hygiene facilities in the giant tank. The challenge of assembling an IKEA station using two fundamentally distinct equipment standards was difficult to excite public attention, unlike the more immediate goals of “following the footsteps of Neil Armstrong.”

Worse, many of the priorities for expanding Enterprise into a permanently crewed station ran directly into the needs of the moon program. With the drive to minimize spending, the Multi-Role Recovery Capsule had emerged as an interim stand-in for a lightweight lunar capsule in many NASA studies for lunar flights. Although it massed slightly less than the command module of the Apollo capsule, the MRRC offered a larger diameter and interior volume, enabling it to carry as many as eight astronauts in a lifeboat configuration. With a smaller crew, the same volume (augmented in most plans by the volume of a lunar module’s cabin) was more than capable of housing two or four astronauts to and from lunar orbit for sortie or outpost missions. With the role of lunar orbit insertion usually delegated to the more efficient thrusters of the lunar lander, only a few tons of added propellant would be necessary to allow the MRRC or an equivalent to return through Trans-Earth Injection. Better yet, the clean and safe ethanol/LOX fuels the Italians had selected for the MRRC to minimize risks of operating it in the Space Shuttle’s payload bay were also nearly passively storable in the lunar thermal environment while providing superior performance to hydrazine engines. Between Bush’s original 90-day study in 1989 and the approval of the Option D lunar program in 1991, this stand-in for a presumed American equivalent gradually became a presumption of partnership with ESA on the lunar program, as the European nations had no intention of being left out of the return to the moon if they could avoid it. Moreover, the MRRC was available sooner and cheaper than any American equivalent, as the first lifeboat missions to Enterprise were planned for 1993 and ESA would contribute the (relatively low) cost of converting the MRRC’s service module for lunar-return operations in exchange for seats aboard the American landers. The agreement was made formal with a memorandum of understanding in the spring of 1992, but had been all but assured for at least four months prior. The result for Enterprise was the hijacking of their lifeboat program. Just as fabrication had begun on the hulls of the first two lifeboats, ESA and the MRRC Program’s NASA liaisons enthusiastically turned to the problems of how to modify the design for the lunar program to the detriment of focus on the first prototypes intended for lifeboat use. Though priority snarls were ironed out over the next several months, the delays to MRRC development would directly push out the date when Space Station Enterprise could operate as more than a crew-tended station.

 

[e of pi]

Boldly Going Part 15

The Minerva program, with its massive investment in new heavy lift vehicles, a new lunar lander, and plans for sustained beyond-Earth exploration meant every activity associated with it had an aura of excitement. Each day brought many new decisions to make to define a new future of exploration, fulfilling promises many at NASA had been made in their youth during Apollo. By contrast, expansion of Enterprise was more work-a-day implementation of plans already under discussion for years, lacking much of the priority or excitement. However, while Enterprise’s refit plans proceeded in relative obscurity on the ground, the station’s crew-tended operations continued full speed ahead in space. Enterprise-bound launches made up half of all Space Shuttle missions, amounting to eleven visits to the station between 1991 and 1993. Some of these missions were routine rotation flights, simply harvesting the station’s power and making use of its facilities as a port of call to extend their own capabilities, with the sum total of on-station activities being the exchange of experiments between the station’s Leonardo Laboratory Module and the visiting Shuttle’s Spacelab or the planned commercial Spacehab module. Others were more ambitious.

Much of STS-49’s record 22 days at the station in August of 1991 was spent on experiments relating to the upgrade of the station itself. The crew rigged wires inside the LOX tank to aid in maneuvering during IVA, then experimented with cutting loose the first unneeded sections of slosh baffle using a power saw fitted with a dust vacuum. Completing the tests was the installation of a mounting system for two dummy Spacelab racks using the system already under development groundside. While the crew was able to install the dummy units, the assembly process was criticized by the crew for its use of nuts and bolts in assembly, requiring both hands to position fasteners then trusting luck to keep one or the other in place while preparing a tool to complete the attachment. Many fasteners were lost in the vast volume of the LOX tank during the process, some to be found in air vent filters years in the future. The installation of a third dummy unit had to be abandoned when the fasteners intended for it had to be used to make up for fasteners lost in the process of assembling the other two modules. While the process of assembling structures on IVA had fewer limits than EVA, as the LOX tank was a shirtsleeve environment, there were still lessons to be learned on the importance of minimizing fasteners and other operations. The program office even began a consulting engagement with designers from furniture-maker IKEA, both on the best ways to package brackets for shipment and the easiest ways to assemble them in space.

While some groups focused on the details of how equipment would be installed into the converted LOX tank aboard Enterprise, another group was faced with a higher-level challenge: how the LOX tank itself would be subdivided into usable volumes. For modules of diameters small enough to fit inside the Space Shuttle, internal layout was relatively easy to establish: a single fly-through passageway down the center of each module, with equipment on four sides. One was typically designated as the “overhead” and another as a “floor.” Though the equipment mounted was often similar, providing these orientation cues was found to offer benefits in reducing space sickness and aiding astronauts in orienting themselves both within a module and within a large structure. Even if equipment in a floor or overhead position required an astronaut to temporarily orient off of the consensus vertical, having the baseline eased astronaut interaction with the environment, not to mention aiding training on the ground. This was experienced on orbit when the “hamster tubes” in the ET-007 External Tank intertank and the access passage into the former orbiter’s middeck caused significant disorientation. Fortunately, these were sections where crew did not typically linger, simply passing through from one section of the station to another.

While the small Shuttle-sized modules were easily divided, with the only question being which direction was “up” for outfitting, the 8.4m internal diameter of the LOX tank was a problem. A single passage and a single lengthwise deck was out. However, vertically stacked decks like those used aboard the 6.6m diameter Skylab would also have challenges, as the distance from a central passage to the walls of the larger 8.4m diameter would be large enough to be of questionable utility. Thus, passages along the axis of the module would need to be off-center to provide for sufficient access to crew quarters, equipment mounts, and logistics stowage. The question was largely if the module should be divided longitudinally, with three decks running horizontally turning the passages along the axis into hallways or if the module’s decks should be stacked along the axis in the transverse orientation, turning the passages into vertical shafts through circular decks [1].



The transverse arrangement had significant Skylab heritage, and the decks would be largely the same in structure from one level to the next, yielding major standardization benefits when launching materials and assembling the pieces in space. Additionally, the slosh baffles located around the edges of the tank would be aligned as circumferential pre-divided lockers for this arrangement and provide natural structural anchor points for the lower several decks. A longitudinal arrangement needed unique deck structures with unique techniques for anchoring to the existing baffles and structures inside the tanks, and the lockers made from baffles on the upper and lower decks would be oriented in ways that were difficult to access. However, NASA’s studies showed that the longitudinal deck layout would provide slightly more effective crew translation through the module. Better yet, the longitudinal deck orientation would match the orientation of the modules in the original OV-101 section of the station, creating a common and relatively consistent “up” for the station’s old and new modules.

To test the concepts, two full sized LOX tanks, sourced from the External Tank Ground Vibration Test Article (ET-GVTA) and the External Tank Structural Test Article (ET-STA) were transported from Houston, where two cradles were built, one allowing one tank to be placed on its end with the nose facing up and the other with it lying on its side. Throughout 1992, both the transverse and longitudinal layouts were tested using mocked-up interiors in their respective tanks. Initially, these mockups were low-fidelity, consisting of large prefabricated decks which were loaded into the tank by the simple expedient of cutting off the ogive nose and fitting it to be bolted instead of welded into place, rendering it something like the nose of the Super Guppy aircraft. The advantages of the longitudinal arrangement for crew circulation and orientation within the station proved to hold up well under the low-fidelity testing, which also revealed a new challenge with the transverse orientation. Ground testing and training would have to take place inside, effectively, a 6-story building and the small decks would require trainees to frequently climb and descend ladders while simulating tasks which might be trivial in orbit. The three stories of the longitudinal arrangement were much safer and easier to navigate even on the ground. Moreover, they could be easily aligned with any future extension into the hydrogen tank, creating three decks running the length of the station, though with an interruption in the middle, instead of another 12 small transverse decks.

Thus, NASA selected the longitudinal arrangement for Space Station Enterprise’s massive new habitation module. Both mockups were converted to the same longitudinal deck configuration by construction of a second horizontal cradle. The original low-fidelity longitudinal mockup was used throughout 1993 and 1994 in finalizing plans for subdividing the decks into working spaces, utility spaces, and stowage, while the new second mockup was used to explore how to reduce the deck frames and structures to elements small enough to transport through the 36” manhole from the intertank tubes and assemble in space. The Shuttle began to transport deck frames to the station over 1995 to prepare for when the first permanent station crew would work to assemble their new habitat. Even as hardware began to launch to space, the two redesignated Space Station Enterprise LOX Tank Outfitting Mockups (SSE-LTOM, pronounced “sell-Tom”) continued to act as pathfinders for the details of assembly. The low-fidelity and high-fidelity SSE-LTOMs became critical for training and procedure development for each crew as they rehearsed installing utilities and consumables stowage, constructing partition walls to divide the deck volumes into rooms and quarters, and installing the furniture and appliances to make them functional habitat spaces for up to 8 permanent crew.

While NASA had been developing the details of their new 560 cubic meter habitat module, ESA and Japan’s NASDA had been working with Johnson on the details of the new lab modules which would enhance the station’s scientific capabilities for the new millenium. The Japanese laboratory would come to take up multiple Shuttle launches, consisting of a large laboratory module capable of holding 10 International Standard Payload Racks, of which Japan would be allocated 6 and their American hosts would be allocated 4, as well as a large exposed facility with a small experiment airlock and a logistics stowage module. The European Lab was smaller, given the spending required by the Multi-Role Recovery Capsule, but would still hold 10 ISPRs, though with less free space for non-ISPR payloads. As the rest of the quid pro quo for their launch, ESA also provided the primary structure for the new US Lab Module, which was a duplicate of the primary structure for the European Lab.

With the decision to have longitudinally oriented decks in the LOX tank volume, it became possible to put the entire station’s main working modules on a common consensus vertical. The only exceptions were the two Japanese-built node modules, which would stick vertically up and down from the two available station APAS ports. Node One, the main expansion node of the station, would be mounted at the bottom of the intertank opposite Enterprise where Shuttles currently visited the station. Node One would provide a new APAS adaptor at its lower end for ongoing Shuttle operation and four radial ports, one for the Japanese lab, one for the European lab, one for one of the station’s two planned MRRC lifeboats (also using an APAS adaptor), and the last for future expansion or the temporary attachment of logistics modules brought by visiting Shuttles. The other node, Node 2, would extend from the APAS port located on the top surface of the Leonardo Lab Module in OV-101’s payload bay. It would also offer five new ports, but only two would be initially occupied. One, facing aft, would play host to the new US Lab Module Destiny, replacing the current primary American lab space in the increasingly obsolete LLM. The zenith axial port would be fitted with a “Pressurized Mating Adaptor” to convert its CBM into an APAS, allowing it to serve as the primary docking port for the station’s other MRRC lifeboat. Having three APAS ports open, split between the ends of the station, helped manage available docking space during crew swaps. With planned crew capacity of 8 and short-duration surge capacity to 12, having an 8-person lifeboat at each end of the station would help ensure the full crew could evacuate the station even if a single module in the long module train was compromised. In one of the only differences from its European near-twin, the US Lab featured an aft axial port instead of the exposed facility the ESA lab mounted, which could be used for short-duration berthing of logistics modules during Shuttle visits to the station. Placing MPLMs on this port, though complex due to the required coordination of the Station and Shuttle’s arms, would allow crews to directly transfer ISPRs into the new US Lab. Because of the complication of this maneuver, the plan was for the US Lab to largely host long-duration ISPRs such as freezers, furnaces, and plant growth experiments, and thus reduce how often it had to be carried out. The port and starboard radial nodes were mostly obstructed from large-scale utilization as they overlapped with the rotation zone of the Enterprise Power Module’s solar arrays after only a few meters. However, the port side of Node 2 provided a perfect vantage point for the station’s new cupola module which fit into the short length available. In the future, NASA planned that if the original arrays became redundant, Node 2’s radial ports could be repurposed for additional station growth.

The two Japanese node hulls were large enough to hold 8 ISPRs each in addition to the four radial ports, but these would generally be used to hold only soft stowage, particularly Node 2, which was separated by dozens of meters of small-diameter corridors and hatches from the rest of the ISPR-equipped modules. This meant that the nodes’ exception to the general station vertical was less critical, as they were largely just used as access passages. The soft stowage of Cargo Transfer Bags could be oriented to match the rest of the station even within the “horizontal” ISPR bays. Before the 1989-1991 indecision in American exploration planning, these modules had seen extensive international design discussion, and both international program’s modules passed through Preliminary Design Review within 8 months of signing the Memorandums of Understanding in 1991 formalizing their involvement in Space Station Enterprise. With the paperwork in hand, conceptual design reviews were completed rapidly. By 1992, fabrication on the first node was underway with launch anticipated within four years.




The remaining American challenge to complete the station’s design was the power requirements of the fully expanded station. The initial Enterprise Power Module generated 50 kW peak for a 25 kW average supply, more than sufficient to power the original modules launched with OV-101 during STS-37R and provide life extension power for a visiting Space Shuttle. However, the completed station would require closer to 250 kW of generating capacity, larger heat dissipation radiators, and bigger batteries to last out orbital nights. The power generation system would need to be extensively augmented to keep up with the growing station. While the EPM was modular and designed to be removed if desired to be replaced with a larger power system, this would require once again risking the station’s future while disconnecting the existing 50 kW EPM and connecting a truss and a new, larger spread of solar array wings.

Once again, creativity would be required to enable the development of the large American station, and once again the answer would be found in the layout of the Space Shuttle’s stack on the pad. The majority of the force from the Shuttle’s two massive Solid Rocket Boosters was carried by a thrust beam located in the intertank of the External Tank, the same beam which the intertank passages were forced to wind around. Each booster was mounted with massive stainless steel sockets and 2.5” diameter explosive bolts to fittings on the outside of the External Tank on each end of the SRB thrust beam. These fittings remained on Space Station Enterprise, and were capable of managing significantly larger forces than would be generated by even the relatively massive truss required for a 250 kW panel system--more than 1.7 million pounds of thrust on ascent and 178,000 pounds of drag after burnout. Better yet, the fittings were far enough forward of the existing EPM to be clear of their rotation zone. A truss extending from the location could be designed such that the existing panels would not need to be retracted for the new set of panels and radiators to be installed. Thus, the existing panels on the EPM could continue to be used while the new truss was built out, or even in parallel with the new truss, only to need retraction in the future to be replaced in-situ when the new truss took over generation and the existing panels aged out of viability. NASA considered the elegant technique of adapting the existing power and data wiring for the SRBs located at the connection points to tie the new truss into the station, but was forced to conclude the systems were not up to the challenges of conversion. Eventually NASA settled on the simpler, if less elegant, expedient of running power cable, coolant lines, and control wiring along the external skin of the ET inside an insulated and debris-resistant conduit. One set would run aft next to the existing ET cable raceway under OV-101, then up and over OV-101’s door sill into the payload bay to interface with the existing EPM hookups. The other set would run down to the new connections to Node 1, allowing the new ISPR modules to directly connect with the newly expanded power system.

With the division of labor for the large new laboratories and node modules among the international partners and American high level plans for the new solar power truss and LOX tank habitat module, the broad strokes of the great expansion of Space Station Enterprise from its OV-101 roots were largely complete. Like a plant growing from a seed, Enterprise would blossom from 200 cubic meters of volume able to intermittently support part of a Space Shuttle’s crew of seven to ten into a whole new station nearly five times the size. In just a few short years, Enterprise should be able to support a permanent crew of at least eight astronauts and occupy their time with three new and more capable laboratories in addition to the relatively limited Spacelab-derived LLM launched with STS-37R. Minerva might be winning all the glory, but work on Enterprise would have just as large an implication for the future of NASA.

[1] These images are from a historical NASA report, which looked at an 8.4m habitat derived from the Exploration Upper Stage (Skylab II). The conclusions may be of interest to anyone else of the “skyscraper orientation” persuasion informed by Atomic Rockets. It’s not a slam dunk for all applications, but with a longer axis than diameter, there are some interesting benefits to having longitudinal decks compared to transverse decks. Give it a read!
http://spacearchitect.org/pubs/AIAA-2013-5433.pdf

Artwork by: @norangepeel (Cass Gibson on Twitter) with support from @nixonshead (AEB Digital on Twitter)

 

[TimothyC]

Boldly Going Part 16

By 1994, the vast majority of the primary design work to define what Congress' 1991 approval of the Option B for Space Station Enterprise’s expansion would mean was complete. However, the modules and systems for the expansion and permanent occupation of the station remained in production and ground testing. In their absence, the station remained functioning purely as a crew-tended vehicle, visited intermittently by Shuttle crews in a way more in line with Skylab than the permanent crews aboard the Russian Mir. While the Russian station was smaller and less capable in almost every scientific capacity, the general public was eager to see NASA finally permanently occupy the station they had spent more than a decade praising and anticipating. The key pacing item was the MRRC lifeboat, the critical safety tool required before a crew could be aboard the station without a Shuttle to take them home. With its conversion to a lunar command module, the lower-aspiration lifeboat had been repeatedly delayed as ESA and NASA struggled with concerns like designing a launch abort system to carry crew free of launches aboard NASA’s new Shuttle-C heavy lifter and the design of a long-duration, higher performance service module capable of trans-Earth injection burns. While these distractions need not have delayed the program if correctly managed, priorities for the lunar program meant that its requirements (earlier in their design cycle) often received focus instead of the execution of assembly support, testing, and certification analysis for the more Earth-bound space station lifeboat. By 1992, the program was more than 8 months behind schedule, and by 1993 this had stretched to more than a year. Still, the first three lifeboat flight articles were finally ready for their test debut in 1994, with the fourth in an advanced state of readiness. By then, the program had gained the official name “Kepler,” as ESA was more willing to embrace a program actively headed for independent crew operations and lunar service, instead of being limited to a lifeboat. The missions for the Kepler vehicle were divided into four classes: Kepler-D would be orbital demonstration missions, Kepler-E would be operational lifeboat rotations on Enterprise carried to orbit and back aboard Shuttle, Kepler-L would be American-launched Kepler capsules used for lunar operations as part of the Minerva program, and Kepler-C would be crewed capsules launched by ESA itself - a dream which would take time to manifest but which ESA already identified as key to the new program as MRRC evolved into Kepler. As another marker of the new significance of the program, each of the individual semi-reusable vehicles was given its own name which would carry over between flights.

The first capsule to fly, the “class ship” Johannes Kepler was flown to orbit in the payload bay of the Orbiter Challenger in June of 1994 for mission Kepler D1, the first orbital demonstration flight. The Johannes Kepler was transported to orbit mounted to the Space Shuttle cargo bay trunnions aft of Spacelab LM2, which was carried both for short-duration experiment capability and to test a logistics configuration for the station, where the space forward of a Kepler could be used for carrying critical station logistics in either Spacelab, Spacehab, or the new Multi=Purpose Logistics Modules which were planned to debut in coming years. Once in orbit, Challenger used her arm to extract the Kepler capsule, and dock its APAS port to the Shuttle’s own port. Next, astronauts Gerharh Thiele and Marianne Merchez boarded the Kepler and activated its systems. After testing core functions such as life support and power generation in tandem with the orbiter’s systems, the capsule was powered down and tested in the loiter mode required for one-year duration rotations on station while the crew conducted other secondary mission tasks in the orbiter middeck and the Spacelab pressurized module. After the test, the crew powered the capsule back up and checked the systems. These tests verified both that all systems had powered down and up successfully and that the temperatures and pressures of the cryogenic ethanol/oxygen propellants had stayed steady within limits in purely passive storage modes. All test results were positive, so the crew moved to the next test: free flight.



With pilots Gerharh Thiele and Marianne Merchez aboard, Johannes Kepler’s APAS port was released from the orbiter and the orbiter backed away to leave the capsule in solo flight. Flying free from Challenger aboard the first European crewed space vehicle, Thiele & Merchez tested their vehicle’s maneuvering thrusters, demonstrating orbital control and formation flights with the orbiter. For Europe, the first European pilots flying a European vehicle in tandem with the American Shuttle was the fulfillment of decades of aspiration, a point of pride, and a sign of more to come, even if they were currently doing so with a variant of the vehicle intended only as a last resort. After docking again, the crew returned to the orbiter. Johannes Kepler would carry on its most critical test alone. The ground remotely commanded the vehicle to release from Challenger’s APAS with no assistance from the Shuttle crew or systems, simulating undocking from a station lacking power or control after some critical failure. Once flying free, Johannes Kepler fired its thrusters and conducted a landing at White Sands Space Harbor in Nevada, demonstrating the ability to safely return astronauts from space. Its task accomplished, the Johannes Kepler was returned to Europe for inspection, replacement of its heat shield, service module, and other expendable components, and preparation for another mission.

Later in 1994, ESA and NASA conducted the second orbital demonstration, Kepler-D2, with the deployment of the Charles Messier from the payload bay of Space Shuttle Atlantis on STS-74 in close formation with Space Station Enterprise. With the only ports available on the station so widely spaced, it was simpler in ESA’s eyes to independently fly Messier to the station, instead of the intended future method of using the shuttle arm to dock the empty capsule to an open APAS port on-station. With such a short-term need for fully automatic onboard docking systems, ESA felt developing automatic docking was unnecessary. Some additional justification for this “cheaping out” came from justifying training at least a few ESA pilots for the first few Enterprise Expeditions and getting them minutes and hours of time commanding a vehicle in space, part of a long-term campaign to get ESA pilots flying Kepler capsules and even American landers on lunar flights. The Charles Messier spent the entirety of Atlantis’s 21 day stay on station quiescent, then ESA pilot Thomas Reiter reactivated it on the Shuttle’s final day on station. The Shuttle and capsule jointly separated from the station to make their own homeward-bound rendezvous. Without the rigors of entry on its heat shield, the requirement to dispose of its service module, or the use of its parachutes, the Messier required much less servicing for reflight. In line with a nominal lifeboat rotation, all the Messier needed to be ready for lifeboat duty was a rigorous inspection and the topping-off of its consumables and tanks.



With both orbital demonstrations carried out, the third Kepler lifeboat, the Edoardo Amaldi, was launched to the station aboard STS-79 in August 1995. Also aboard the Space Shuttle Atlantis for the launch were the first permanent crew of Space Station Enterprise, led by station commander Robert L. Gibson, a naval aviator nicknamed “Hoot.” When the Amaldi was making its flight between the Shuttle Atlantis with ESA astronaut Thomas Reiter back at the controls, Gibson insisted on his entire 4-person crew joining the short transfer flight, therefore delivering themselves the final miles to their new station. When Atlantis arrived after a rendezvous extended by minor electronic issues with the Shuttle’s radar system, “Hoot” greeted them at the hatch, offering them permission to come aboard, and enquired what had kept them so long.

Along with the Amaldi, a double Spacelab module carried the latest supplies intended for the station’s first crew. More than just consumables had been pre-positioned over Enterprise’s previous 5-years of operation, as the flights had carried up literal tons of the structural elements to be used for the planned LOX tank conversion. The LOX tank had slowly been brought up to full atmospheric pressure, and several sequential Shuttle flights had ferried building materials for stowage inside the vast tank. Gibson’s 4-person Enterprise Expedition 1 crew was largely kept busy by the tasks of routine station maintenance and the assembly of its newest expansion. Therefore, only on average one crew member was available to handle the scientific experiments stored in the Leonardo Lab Module. However, considering scientists on the ground had five years of experience operating experiments with only intermittent crew support at all, this was still a noticeable improvement.

The rest of Gibson’s crew set to work on the assembly of the new decks to subdivide the LOX tank, beginning by assembling the struts clamped to the baffles which would provide the main vertical support columns between the decks, then assembling the deck floor between the columns along the length of the module. The experiences with the early attempts to install experimental modules in the simulated mounts in 1992 and procedures developed in the SSE-LOTM simulations on the ground paid off--the modules were mostly assembled using clips and mallets instead of nuts and bolts, but some fasteners were still needed at each of the hundreds of connections making up the support columns and deck floor modules. The result was the use of fasteners by the bagful. To encourage his crew to avoid losing critical fasteners inside the tank’s massive volume, “Hoot” had worked with ground crew on a surprise: motivational posters in the style of WWII recruiting images, bearing labels like “Give a Hoot, Don’t Pollute” and “Avoid Getting Screwed--Don’t Let Your Fasteners Bolt”. By the end of Gibson’s four-month Expedition 1, the vertical columns were all installed and the majority of the deck modules on-station had been assembled, completing the Main Deck. The dimly-lit cavern which Garriott and Thuot had explored on STS-38R now five years later bore a resemblance to a modern office building under construction as interpreted first by MC Escher and then by IKEA. Gibson turned over the ongoing outfitting process to Ken Bowersox’s Expedition 2 in January of 1996. Both naval aviators, Gibson summed up his final spaceflight when he greeted Bowersox’s crew on their arrival at the station in the Space Shuttle Columbia. “As one Captain to another, welcome aboard my proudest command--the Enterprise.”

Artwork by @nixonshead (AEB Digtial on Twitter)

 

[e of pi]

Boldly Going Part 17

After taking over command of the station, the second permanent crew of Space Station Enterprise settled into their new home. The work of outfitting the LOX tank continued to consume the crew’s time as a top priority. The early Enterprise expeditions were well-motivated, as they were literally building their new home. Until the new habitat section was complete, they continued to bunk in the Shuttle-adapted sleep stations in OV-101’s middeck, which also served as galley and was home to the station’s only lavatory. This additional space had seemed vast when some expedition crews had previously used them when visiting the station short-term aboard Shuttle flights...when they had the benefits of an entire second Orbiter’s middeck, lavatory, and typically another Spacelab or Spacehab module. With no second orbiter beyond the intertank’s docking hatch, the crew of four had barely more space than any pre-Enterprise Space Shuttle mission, but were now embarked aboard for a mission months in duration. The counterbalance of the massive open LOX tank volume was cited by many of the crew as key ammunition against cabin fever given the cramped confines of their existing habitat in the old orbiter portion of the station, even as it consumed workday after workday.

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The arrival of STS-83 in June 1996 was a welcome relief for Expedition 2 both from the cramped confines of the primary habitat spaces and from the daily routine of assembling hardware and tracking down loose bolts inside the LOX tank. The orbiter brought with it the first permanent addition to the station, the Japanese-built Node 1 module. Fitted with an APAS port at each end and four radial CBM ports, this module once attached to the nadir port on the station’s intertank would be the core of the nadir ISPR section of the station. There, it would eventually host the new European and Japanese laboratories which were still under construction. In addition to this role in future growth, Node 1 also served a critical immediate need which was highlighted by the complexity of its own arrival. At launch, Space Station Enterprise had just two APAS ports. With one taken up by Shuttle and one by the current Kepler lifeboat, there was neither room to rotate crew return vehicles, nor a place to lock the larger new Multi-Purpose Logistics Modules (MPLMs) which Europe was building for Shuttle logistics flights. In the meantime, Spacelab and the commercial Spacehab modules had to suffice, with cargo brought through the Shuttle’s APAS docking port. The issue was that Shuttles arriving at station docked to the adapter on the same nadir intertank port which Node 1 was intended to dock to. Thus, a complex ballet was required for Challenger to deliver the new Node. Before arriving at the station, Challenger’s crew extracted the node and pre-docked the future zenith end to the Shuttle’s docking port, and then flew the node into docking at the nadir end of the existing adapter in one of the trickier docking maneuvers of the Shuttle program’s history. During STS-83’s short stay on the station, only limited work was done to set up the new module. Once the Shuttle left, Expedition 2 were then free to disconnect the zenith end of the existing adapter from the intertank’s APAS port. Using CanadArm 2, the station then flipped the adapter-and-Node subassembly end-for-end and reattached it. Node 1 was thus in its final configuration, and then the adapter module was detached from Node 1 and flipped again. This complex “Towers of Hanoi” puzzle left the adapter once more right-side-up, but now at the nadir end of Node 1, ready to receive the next orbiter and with 4 more ports open on the sides of Node 1.

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Comparing the relatively small number of crew-hours required to finish installing and outfit the new Node 1 with the much large number required to build the LOX tank habitat in-situ provided major ammunition to those recommending against the incorporation of wet-lab tank adaption into future projects, primarily on the Moon but also for future missions to Mars or beyond. However, advocates of those techniques also pointed out that while the outfitting process would end up consuming the complete attention of five Enterprise Expeditions between August 1995 and May 1997, the result was a station which could barely have been launched any other way. Over roughly a year and a half, the vertical columns and hand-grip wires spanning the cavernous tank had turned into decks, then the framing that defined future walls. Much like building a house on Earth, those frames had been filled by a complex and well-thought-out maze of wiring, plumbing, and ducts. With the labyrinth of utilities installed, the partition walls had been finished by adding their outer foam board and fabric coverings, then stowage racks, equipment bays, and furniture had been installed into the newly divided spaces. By the spring of 1997, the new module’s basic life support systems were active and the crew were sleeping inside the former LOX tank, with the expanded crew quarters allowing Expedition 4 to be augmented to become the first 8-person crew aboard the station with the arrival of four more crew members who would rotate on into Expedition 5. The jump in available hands and the morale benefits of rapidly approaching completion helped accelerate the process, and the work inside the LOX tank was largely done by the time Expedition 5 took over the station in the summer of 1997.

The laborious work of outfitting the Enterprise Habitat Module inside ET-007’s former LOX tank was only part of the work carried out to ready the station for expansion in 1997. In addition to work inside the station’s pressure volume, Expedition 5’s expanded crew also conducted EVAs to run some of the external cabling for the new port and starboard truss modules to their future mounting points on either side of the intertank. This productivity was driven, in part, by the fact that the additional personnel had little scientific work competing for their attention. The station’s lab equipment was still contained in the single Leonardo Lab Module, by 1997 as often known by crews as the “Old Lab” as by the acronym “LLM” or the former slang term “LeoLab.” When the truss modules, and the labs whose power systems they would support arrived over the next two years, Space Station Enterprise would once again raise the bar for orbital outpost capabilities. In the meantime, the crew had little to compete with their day-to-day tasks of tending a few experiments, routing cables, assembling furniture and exercise equipment, and testing systems. Their recreation options had expanded tremendously in the new Enterprise Habitat Module, and Space Station Enterprise became known as a place which worked hard, but also played hard. Beyond a robust litany of pranks played within the crew, on ground control, and visiting Shuttles, the crew enjoyed swapping stories in the galley, and also a long list of higher technology entertainments. The crew could watch movies and television recordings on the station’s new VHS video player, which although intended partially for training was recognized as a critical entertainment device to prevent boredom on long rotations. Tapes of Hollywood films, recent television, and sports events were prime fodder for the on-station barter economy when Space Shuttle crews visited. They could also enjoy a limited selection of board games, listening to music on compact disc, and making their own music with the station’s collection of musical instruments. Even the station’s collection of laptops, primarily intended for updating schedules and reviewing documents, could be used for playing games like Minesweeper, Solitaire, and Microsoft’s ubiquitous “Space Cadet” pinball.

The outfitting of the new habitat module and the cycling of permanent crews also began to build up new collections of decorations. “Hoot” Gibson’s two posters had been joined by other wall decorations, ranging from posters of Hubble Space Telescope images to the mission patches of various Enterprise expeditions and Shuttle missions which had visited the station. The roof of one of the longitudinal hallways past the crew quarters on the main deck was graced by dueling posters of the crews of the Enterprise from the original series and Star Trek: The Next Generation. An attempt to replicate Skylab crew’s practice of running laps around the station’s diameter in the large forward exercise bay and the aft translational dome of the habitat module brought reprimands for the crew of Expedition 6, as it disturbed the microgravity of experiments aboard the station. While the vibrations of assembly and outfitting were tolerable as long as it happened, they had to be minimized now that the station’s plush new habitat was finally largely complete.

The luxurious new accommodations and amenities drew rave reviews from crew aboard the station. During the mid-to-late 90s, several astronauts within NASA’s corps and much of ESA’s French astronaut complement had the chance to fly to the Mir space station. The Americans made their visits aboard the Space Shuttle during the Shuttle-Mir Program, a series of short-duration visits of the Space Shuttle to the Russian space station which were in many ways a follow-up to the Apollo-Soyuz Test Project. The flights, and equivalent exchange flights of Russian cosmonauts to Enterprise for short duration stays on the station, were aimed at enhancing relations with the post-Soviet Russian Federation and ensuring none of their rocketry experience leaked into the hands of rogue states.

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The French flights to Mir, by contrast, were not short duration visits by any means, but instead an ongoing project demonstrating European independence from NASA planning. As a result of CNES’s frustrations with deferred American station planning in the early part of the decade, the late 1990s saw the launch of the station’s Priroda laboratory, one of the originally planned TKS-based lab modules which was completed and launched thanks to CNES funding. In exchange for the module’s funding, France received several experiment spots aboard the station, which were then visited by a succession of French astronauts aboard Russian Soyuz capsules embedded with long-duration Mir crews, some of whom had previously flown aboard Shuttle or Space Station Enterprise. Those which had not already done so before flying to Mir were likely to do so after, given the demand for crew during the busy period outfitting the LOX tank Habitat Module aboard Enterprise between 1995 and 1997. Mir’s facilities were limited, even for the crews of 3 typically aboard, and even two Russian exchange astronauts who visited Enterprise aboard STS-95 during 1997 had to concede that the incomplete Enterprise still offered larger crew spaces and more capability for hosted experiments. While the new Habitat Module was more spacious, some areas like the “hamster tubes'' were nearly as cramped as their equivalents aboard Mir. Still, unlike Mir, Enterprise was growing, and the new laboratories would be a major step forward in capability, helping to justify the expanded crew habitat spaces and power generation facilities.

The challenge lay in getting those new modules launched as the lunar program ramped up. Enterprise’s first-and-only launch from Kennedy Space Center had required the activation of a third High Bay in the Vehicle Assembly Building, meaning that NASA had the ability to stack three STS launchers at the same time, whether those be conventional Space Shuttles or the new Shuttle-C. Consideration was given to activating the VAB’s fourth High Bay, bringing it to a level of capability never even seen during Apollo. Ultimately it was decided to be too costly to be worth the expense, given the need to have someplace in or near the VAB for vertical checkout of External Tanks newly arrived in Florida. Besides, pad utilization limits would have allowed only a small boost in launch rates from four integration cells before new limits were imposed by launch site availability [1]. However, the requirement to have a rescue orbiter available for launch-on-need for any missions not going to an orbit at least coplanar with Space Station Enterprise meant that in practice there was only room for one of the new Shuttle-C launch vehicles to be prepared at a time if a Space Shuttle launch was to happen within the next month or so. Two Shuttle-C launches were required for a 2-person, 4-day sortie mission to the moon, and a full four launches would be required in two campaigns for more-extended 4-person, multi-month “mini-base” missions. Even testing these procedures required cutting large gaps into the Space Shuttle launch cadence, Thus, NASA mission planners had to carefully balance the requirements and timing for test flights of Shuttle-C and lunar hardware, science missions and payload deployment missions by the Space Shuttle not headed to Enterprise, and Space Shuttle launches carrying crew, supplies, or new modules to Enterprise.

The effect was like trying to keep three or four plates spinning on the ends of rods--every plate needed to be refreshed as it spun down, but little more attention could be paid to each than the bare minimum. If any program was “first among equals,” it was the lunar program. Even with the replacement of President George H. W. Bush with President Clinton, the multinational lunar program proceeded with a high level of priority. Though unofficial, almost all of NASA and the political atmosphere surrounding the agency continued to place a high value on the return to the moon happening in time for the 30th anniversary of the Apollo landings in 1999. When originally authorized by Congress in 1991, it had been expected that the Shuttle-C vehicle could draw on the legacy of Enterprise’s launch on STS-37R to target a 1996 introduction into service, allowing extensive time for testing ahead of the debut of lunar hardware. Unfortunately and perhaps unsurprisingly, the scope of the vehicle had increased to match the time allowed before the first lunar landers and lunar-bound Kepler spacecraft would be available.

Artwork by: @nixonshead (AEB Digital on Twitter)

[1] Typical timing for a Shuttle mission in the mid-90s historically, taken from data in Jenkins (III-410 to III-413):

SRB stacking typically took 18 to 21 days, during which much other work in the entire VAB must be stopped, notably including prep for ET or Orbiter mate in other cells. ET mate and preparation for orbiter mate appears to have been about a week, although this was often interrupted by SRB segment stacking for other, later, flights and would result in pauses measured in weeks or months between SRB stacking and ET and orbiter-mate. Orbiter mate to rollout was often about a week. Time on the pad prior to launch was typically about 24 to 35 days, excluding particularly protracted stays. This gives about 6 weeks total in the VAB, for about 17 per year as a theoretical maximum, though @TimothyC has a recollection a practical limit was considered more like 14/year (from Shuttle and Shuttle-C study work in the late 1980s and early 1990s). This matches with the rough time in the Orbiter Processing Facility (~60-100 days) which limits each orbiter to closer to 4 flights per year, for about 12-16 for the fleet.

With LRBs and Shuttle-C slotting in, those limits change a lot. It’s about three weeks in the VAB, with no limits on work in adjacent cells, meaning three VAB cells can generate about 50 flights/year, in theory. In practice, that number would be lower, but even with two launch pads, a flight every 35 days per pad is still only about 28 flights per year meaning pads, and more specifically MLPs, and not VAB cells, is the new limit.

As far as @TimothyC sees, the fastest turn around of a launch pad in the program history was 410 hours (just over 17 days) between the launches of STS-51-D and STS-51-B in April of 1985. Given that the pad infrastructure needed to be checked after each exposure to the SRB exhaust, this can be treated as the fastest a pad (but not an MLP) can be turned around. The stack used on STS-51-B had been prepared for the STS-51-E Mission in March of 1985, but was rolled back to the VAB due to concerns with the planned TDRS-IUS payload. A payload that would eventually be remanifested on STS-51-L both OTL, and ITTL. LRB exhaust reduces the wear to the MLPs, though not to a degree where we can quantify the upper limits.

There’s still only about 12-16 Orbiter availabilities per year, but Shuttle-C would be able to fly another 3-4 flights per year per reusable OPAM. The core of all this, then, is that with Shuttle-C added to the Shuttle rotation and LRBs significantly reducing time in the VAB, STS can support pretty much any flight rate NASA can afford to utilize, well into the double digits, as long as a significant number of them are Shuttle-C.